test: Add find_all and configurable clicks to the UI test harness

[AncientPixel]

Description

UI integration tests could neither count repeated local IDs nor exercise clicks with modifiers. This adds collection queries and configurable native clicks through the existing TestWindowExt trait. The new required methods are an intentional breaking change for downstream trait implementations.

• TestWindowExt::find_all returns every registered matching snapshot, including invisible elements. Results follow the current frame's bounds origin (y, then x); equal-origin order is unspecified. This is geometry, not stable identity, paint order, or business order. Existing unique queries still reject ambiguous IDs.
• TestWindowExt provides click_with_options and a centered click_with_modifiers convenience method. ClickOptions combines local offset, mouse button, positive click count, and modifiers using private fields and builders.
• Configurable clicks dispatch modifier-change events when needed, carry the requested modifiers through move/down/up, and restore the previous modifier state afterward. Caps lock is preserved. Existing convenience methods retain their behavior.
• ScopedWindow exposes the same new capabilities inside its identity scope.
• English, Chinese, and skill documentation describe imports, configuration, state restoration, and snapshot ordering/visibility boundaries.

For example:

use gpui_kit::test::{ClickOptions, TestWindowExt};

let options = ClickOptions::new()
    .with_offset(point(px(8.), px(8.)))
    .with_button(MouseButton::Right)
    .with_count(2)
    .with_modifiers(Modifiers::shift());
window.click_with_options("row", options, cx);
let visible_count = window.find_all("notification")
    .iter().filter(|element| element.visible()).count();

This change was written with AI assistance (Claude Code and OpenAI Codex).

Public API

gpui-kit::test

• TestWindowExt::find_all(&self, id: impl Into<ElementId>) -> Vec<ElementSnapshot>: all registered matches from the last completed frame; empty when absent.
• TestWindowExt::click_with_options(&mut self, id: impl Into<ElementId>, options: ClickOptions, cx: &mut App): dispatches a configured click and restores modifier state.
• TestWindowExt::click_with_modifiers(&mut self, id: impl Into<ElementId>, modifiers: Modifiers, cx: &mut App): default method for one centered left click with modifiers.
• pub struct ClickOptions: caller-owned click configuration with private fields; implements Clone, Copy, Debug, and Default.
• ClickOptions::new() -> Self: creates a centered single left click without modifiers.
• ClickOptions::with_offset(self, offset: Point<Pixels>) -> Self: sets a local offset from the target's top-left corner.
• ClickOptions::offset(&self) -> Option<Point<Pixels>>: returns the offset; None means center.
• ClickOptions::with_button(self, button: MouseButton) -> Self: sets the mouse button.
• ClickOptions::button(&self) -> MouseButton: reads the mouse button.
• ClickOptions::with_count(self, count: usize) -> Self: sets the click count; panics for zero.
• ClickOptions::count(&self) -> usize: reads the positive click count.
• ClickOptions::with_modifiers(self, modifiers: Modifiers) -> Self: sets the modifiers for the sequence.
• ClickOptions::modifiers(&self) -> Modifiers: reads the modifiers.
• ScopedWindow::find_all(&self, id: impl Into<ElementId>) -> Vec<ElementSnapshot>: collection query restricted to the scope.
• ScopedWindow::click_with_options(&mut self, id: impl Into<ElementId>, options: ClickOptions, cx: &mut App): configured click restricted to the scope.
• ScopedWindow::click_with_modifiers(&mut self, id: impl Into<ElementId>, modifiers: Modifiers, cx: &mut App): centered modified left click restricted to the scope.

gpui-base::test_support (internal, #[doc(hidden)])

• find_all(window: &Window, scope: &[ElementId], id: &ElementId) -> Vec<ElementSnapshot>: lookup behind Kit's collection queries.
• Existing find(window: &Window, scope: &[ElementId], id: &ElementId) -> Option<ElementSnapshot> delegates to the shared lookup and retains its ambiguity assertion.

Breaking Changes

TestWindowExt gains two required methods: find_all and click_with_options.
Downstream implementations must implement both. click_with_modifiers has a default
implementation through click_with_options. Call sites continue to import only
TestWindowExt for all window queries and interactions.

 impl TestWindowExt for MyTestWindow {
     // Existing methods remain.
+    fn find_all(&self, id: impl Into<ElementId>) -> Vec<ElementSnapshot> {
+        self.window.find_all(id)
+    }
+    fn click_with_options(&mut self, id: impl Into<ElementId>, options: ClickOptions, cx: &mut App) {
+        self.window.click_with_options(id, options, cx);
+    }
 }

Validation

Linux validation:

• cargo check -p gpui-kit --features test-support --tests --locked
• cargo test -p gpui-kit --features test-support --test interactions --test window --test collections --test overlays --locked
• cargo clippy -p gpui-kit --features test-support --tests --locked --no-deps -- -D warnings
• cargo fmt --all --check
• git diff --check

Regression coverage checks modifiers on pointer events, modifier-change callbacks and restoration of both neutral and pre-existing states, combined offset/right-double-click/Shift on both window and scoped APIs, configuration defaults and invalid zero counts, repeated-ID scope filtering, and stacked notifications. macOS and Windows validation remains with CI.

[AncientPixel]

The failing GPUI Fast (windows-latest) check isn't from this change. It fails at link time with LNK1123: failure during conversion to COFF, the same way it fails on main at c0bebdc, the commit this branch is based on. #3380 looks like the fix. Once it lands I'll rebase onto main so CI runs again.