display(iOS): fix touch gestures and add drag to scroll mode

[osy]

This is a rewrite of #7697 by @ifilipis. That PR identified real problems with touch input on iOS, but it arrived as one 900-line commit that also changed defaults and switched existing gestures off for current users. This branch keeps the fixes, splits them into one commit per issue, and leaves the existing touch modes and all defaults as they are.

What changes

1. Long press works after half a second. The long press waited for the tap recognizer to fail, which only happens after the finger has been down for 0.75 to 1.5 s depending on the iOS version. A normal long press came out as a tap, so "Right Click" produced a left click or nothing and "Click & Hold" never pressed the button.
2. Pans start at once. Every pan waited for the three finger keyboard swipes to fail, which takes up to half a second. Moving the cursor with one finger or scrolling with two did nothing for that long, and a short two finger scroll was mostly lost. The pinch no longer waits either; instead it may not begin while three fingers are down, because before iOS 18 it begins with two of three fingers and takes the touches from the keyboard swipe (that also stops three fingers from zooming on those versions). When two finger pan and two finger swipe both scroll the wheel, they now run together and the swipe follows "Invert Scroll".
3. Touches that start at a screen edge reach the guest. A drag from the top edge pulled down Notification Center and the guest saw nothing. Uses SwiftUI's defersSystemGestures(on:) (iOS 16+) next to the existing persistentSystemOverlays(.hidden). On iOS 18 and later a swipe up from the bottom edge still goes home, because the system ignores the deferral while the home indicator is hidden.
4. Middle click and right/middle drag. "Middle Click" for long press and two finger tap, "Right Click & Hold" and "Middle Click & Hold" for the two and three finger pans. New values for existing settings; defaults unchanged.
5. New "Touch mode (drag to scroll)". In the existing touch modes the left button goes down the moment a finger lands, so every two finger tap, scroll or pinch starts with a left press and a short drag at the first finger (selected text, stray marks, accidental clicks). The new mode never presses on touch down: a tap clicks, one finger drags the content, a long press runs the long press action, and a long press that moves becomes a left button drag. A ring shows when the long press is recognized. A quick second tap close to the first clicks on the same spot so the guest sees a double click.
6. A cancelled drag releases its button. When the system takes over a touch that is holding a button (for example a long press drag that turns into the swipe to go home), the guest was left with the button held down.

Claims in #7697

#	Claim in #7697	Here	Notes	Simulator	Tested on device
1	Conflicts everywhere: scroll triggers pinch and taps	Partly	The stray left press is gone in the new mode; the old touch modes keep it by design, since there the touch is the drag. "Scroll triggers pinch" did not reproduce.	Yes	Yes
2	Gesture types very limited	Yes	Middle click, right and middle hold.	Yes	Yes
3	Scroll only triggers after dragging across half the screen	Yes	First scroll event from 0.48 s to 0.17 s, first cursor motion from 0.52 s to 0.07 s, in every mode.	Yes	Yes
4	Undocumented, unconfigurable gestures	No	The three finger keyboard swipe and pinch-with-Move-Screen still have no setting. The PR's settings defaulted to Disabled, which turned both gestures off for existing users.	n/a	n/a
5	Old touch mode conserved, new mode added	Yes	The old modes are untouched here. In #7697 they were not: pinch and the keyboard swipe were off by default and the per-swipe wheel stopped working.	Yes	Yes
6	Tap / click works the same way	Yes	Plus the double tap fix above.	Yes	Yes
7	One finger drag scrolls, no erroneous clicks	Yes	Content follows the finger (the PR scrolled the other way), and a touch stops a fling.	Yes	Yes
8	Long press right click with a visual indicator	Partly	Indicator included, and the underlying bug is fixed in every mode. The default stays "Click & Hold".	Yes	Yes
9	Long press + drag does a left drag	Yes	Without the PR's extra setting.	Yes	Yes
10	Two finger tap clicks at the first touch	No	Still clicks midway between the fingers, as on main.	n/a	n/a
11	Two finger drag resolves conflicts, no delay	Mostly	Starts at UIKit's normal 10 pt threshold. A multi finger drag still moves the cursor to the point between the fingers.	Yes	Yes
12	Two finger swipe resolved correctly, fine-tunable	Differently	Keeps UISwipeGestureRecognizer; pan and swipe run together when both scroll. The PR's velocity based detection was left out.	Yes	Yes
13	Pinch based on absolute finger travel	Left out	A 10 pt finger drift during a pan does not start a pinch, so there was nothing to fix.	Yes	Yes
14	Pinch is two fingers only	Yes	Needed before iOS 18, where three fingers zoomed; see change 2.	Yes	Yes
15	Same fixes for three finger gestures, swipe in settings	Partly	The three finger pan gets the new actions but still waits for the keyboard swipe (about 0.3 s), since both use three touches. No three finger tap or swipe settings.	Yes	Yes
16	Gestures persist once one has fired	UIKit	Left to the recognizers' own exclusion. Cannot be simulated (see Testing).	No	Yes
17	New mouse events: left, right and middle drag plus clicks	Yes	See change 4, plus change 6.	Yes	Yes
18	Fixed gestures near the screen edges	Yes	With the SwiftUI modifier instead of patching UIViewController; the patched getter was ignored on iOS 17.	Yes	Yes
19	Defaults changed to match MS RDP	Left out	Would change behaviour for every user who never opened Settings.	n/a	n/a
20	Nothing in the driver changed	Same	Only Platform/iOS.	n/a	n/a

Resolves #4738

Testing

Testing: Tested by a human on iPhone 16 Pro, iOS 26.7. The author acknowledges that this change has been tested and/or reviewed by a human in accordance with UTM's AI contribution guidelines.

The device test covered 22 steps over four settings configurations: all defaults in Drag cursor mode, the new mode with the new actions, the old touch mode with pan and swipe bound to different actions, and long press disabled. It included the cases that cannot be simulated: three finger swipes and two finger gestures with the fingers landing at different times. One step was skipped (Apple Pencil with palm rejection, and an external pointer, while the new mode is selected). The first device pass found that double tap did not work in the new mode; that is fixed in change 5 and was retested.

Automated testing, in addition: every change was run before and after on iPhone simulators with iOS 17.0, 18.0, 26.0 and 27.0, against a Windows XP guest. A UI test bundle injected synthetic multi finger touches, and a local logging shim (not part of this PR) recorded the mouse events sent to the guest and the recognizer state changes. iOS 18, 26 and 27 agree on every check. iOS 17 differs, which is where the pinch guard in change 2 and the SwiftUI modifier in change 3 came from. Synthetic touches land all fingers at the same instant, so staggered landing was only tested on the device.

Not tested: iOS 15 and 16 (on iOS 15 change 3 has no effect, the modifier needs iOS 16), iPad, and visionOS (the modifier is unavailable there and compiled out; the visionOS target was not built).

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