Compute the paragraph drawing frame at mount time, not in layoutSubviews

[janicduplessis]

Summary:

RCTParagraphComponentView derives the text view's frame and drawing frame in layoutSubviews, requested with setNeedsLayout from updateState and updateLayoutMetrics. The layout pass itself dates from #46081, but until #57408 drawRect: read the content frame straight from _layoutMetrics, which is always current; #57408 moved drawing onto a drawingFrame computed in layoutSubviews, so drawing now assumes a layout pass will run before the view is displayed. It does not when the mount itself happens inside Core Animation's display phase — which is where AppleEventBeat processes a synchronous event requested during layout (#58530). This transaction's layout pass is already over, so the text view displays the new attributed string in the previous drawing frame and the text is cut off at the old width. The queued layoutSubviews updates the frame in the next transaction, but drawingFrame is a plain property that does not invalidate the display, so the clipped drawing stays until something else redraws the view.

Nothing on main emits a synchronous event from layout yet, so this is latent today; #58109 is the first thing that does (layoutSubviews reporting safe area insets on rotation) and it hits this on every rotation.

The frames are now computed in finalizeUpdates:, which the mounting manager calls once per view after all of a mutation's update* calls. That coalesces state and layout-metrics changes the same way the layout pass did — one computation per mount, as before — without depending on a layout pass that may already have happened, and it removes the extra layout pass altogether. The layoutSubviews override goes away; updateState and updateLayoutMetrics keep their setNeedsDisplay.

Changelog:

[IOS] [FIXED] - Text no longer renders clipped when mounted from a synchronous event during layout

Test Plan:

Reproduced with #58109 on top of this branch, RNTester "Safe area insets" example, iPhone 17 Pro simulator: present the padded modal, apply insets, rotate. The readout text is re-rendered synchronously from the rotation's layout pass.

Before	After

Before: top: 0, right: 62, bottom: 19.99996 — the accessibility label carries the full …9482421875, left: 62, and the layout box is the right size; only the drawing is cut at the previous width. The paragraph under it overflows on one line for the same reason. After: both render at their new width. Rotating back to portrait renders correctly too, and ordinary text throughout RNTester (normal asynchronous mounts) is unchanged.

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Found while testing #58109, which hits this on every rotation; standalone, that stack does not include this change.

[meta-codesync]

@Abbondanzo has imported this pull request. If you are a Meta employee, you can view this in D121209981.