[Gtk4] Support MenuItem images on GTK4

[akurtakov]

GtkModelButton (GTK4's native menu row) never shows both an icon and
text, so menu items with images rendered without their icon. Work
around this by embedding a custom icon+label(+accelerator) GtkButton
into the popover via gtk_popover_menu_add_child() for PUSH and CHECK
items. The custom row uses the "modelbutton" node name so the menu row
rules apply to it, and announces itself as a menu item like
GtkModelButton does. Its leading box and the native rows'
indicator boxes share one GtkSizeGroup, so icons and the check marks
of native CHECK rows sit in one column and all labels line up. CHECK
rows carry a GtkCheckButton bound to the item's action in front of the
icon, and while a menu has such a row the other custom rows keep that
check column in front of their icons, so the icons line up too;
CASCADE and RADIO items keep the native GtkModelButton.

The custom rows take part in the popover's row selection sync through
the "selected" state the theme paints, and hovering one closes a
sibling's open submenu after a short delay, as GtkModelButton does.

Injection is self-healing: GTK's "custom" ids are single-use, so a
detached or rebuilt row is re-injected under a fresh id.

Contributes to #2511

[github-actions]

Test Results

  212 files  ±0    212 suites  ±0   25m 11s ⏱️ - 3m 22s
4 959 tests ±0  4 932 ✅ ±0   27 💤 ±0  0 ❌ ±0 
7 187 runs  ±0  6 996 ✅ ±0  191 💤 ±0  0 ❌ ±0 

Results for commit befbf90. ± Comparison against base commit c93196d.

♻️ This comment has been updated with latest results.

[Copilot]

🟡 Changes recommended

HiDPI sizing, accessibility semantics, theme overriding, and integration coverage need correction.

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Pull request overview

Adds GTK4 menu-item images using custom popover rows while preserving alignment, selection, actions, and submenu behavior.

Changes:

• Adds custom image-capable PUSH and CHECK menu rows.
• Adds GTK4/JNI APIs for custom popover children and sizing.
• Re-enables the GTK4 image test.

File summaries

File	Description
Test_org_eclipse_swt_widgets_MenuItem.java	Re-enables image API testing.
MenuItem.java	Implements custom image menu rows.
Menu.java	Injects, aligns, and synchronizes custom rows.
Display.java	Adds custom-row highlight styling.
GTK4.java	Declares required GTK4 APIs.
OS.java	Declares supporting GLib APIs.
GTK.java	Declares widget construction and CSS APIs.
os.c	Adds generated JNI implementations.
os_stats.h	Updates generated OS JNI statistics.
gtk4.c	Adds generated GTK4 JNI implementations.
gtk4_stats.h	Updates generated GTK4 JNI statistics.

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 4
• Review effort level: Balanced

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[Copilot]

🟡 Changes recommended

Custom-row highlighting, CHECK accessibility state, and teardown state handling remain incomplete.

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Review details

• Files reviewed: 11/11 changed files
• Comments generated: 3
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

Image-bearing CHECK items regress native Space-key behavior by closing the menu.

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Review details

• Files reviewed: 11/11 changed files
• Comments generated: 2
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

The complex native row lifecycle lacks regression coverage beyond basic image property storage.

Get a fresh assessment by requesting another Copilot review.

Review details

• Files reviewed: 12/12 changed files
• Comments generated: 1
• Review effort level: Balanced

[akurtakov]

Good enough state for initial support. Whatever problems are found from now on should be handled in separate issues/PRs