Find/Replace overlay: adopt Eclipse command infrastructure for shortcuts and enablement

[HeikoKlare]

Motivation

The Find/Replace overlay currently dispatches its keyboard shortcuts through custom SWT KeyListeners and toggles button enablement by manipulating ToolItems directly. This bypasses the Eclipse key binding framework entirely:

• Shortcuts cannot be seen, or customized, via Preferences > General > Keys — the overlay's operations don't show up there at all today.
• Any user-defined key binding override is silently ignored, since the overlay never asks the binding framework what key is currently bound to a given operation.
• Button enablement and shortcut hints are pushed onto widgets imperatively from several call sites, rather than being derived from a single source of truth.

This continues the incremental refactoring of the overlay's command handling started in #4164, #4169, #4176, #4178, #4184, and #4185 (see "Builds upon" below): now that a dedicated FindReplaceOverlayCommandSupport class owns all the overlay's command-related infrastructure, this change lets it take the next step and represent every overlay operation as a genuine Eclipse handler.

Contributes to:

• Find/Replace Overlay: Allow rebinding shortcuts #2015 (allow rebinding shortcuts)
• [find/replace overlay] Separate UI from Controller Logic #1912 (separate UI from controller logic)

Concept and design

Actions become handlers. FindReplaceOverlayAction now extends AbstractHandler, so every overlay operation (search forward/backward, replace, toggle options, close, ...) is a real Eclipse handler that can be registered with the command framework. AccessibleToolItem.setAction() derives a ToolItem's enabled state (via IHandlerListener) and its shortcut-hint tooltip (resolved through IBindingService) from the action itself, instead of having both pushed to it explicitly at each call site.

A dedicated key-binding context hierarchy is declared in plugin.xml and activated/deactivated together with overlay focus, so that search- and replace-specific commands are only reachable while the corresponding input field has focus:

findReplaceOverlay                      (parent, active whenever the overlay has focus)
├─ findReplaceOverlay.searchFocused     (active while the search field has focus)
└─ findReplaceOverlay.replaceFocused    (active while the replace field has focus)

Handler activation is registered once per action, scoped by an ACTIVE_FOCUS_CONTROL-based Expression — backed by IFocusService tracking the search/replace text controls — rather than being imperatively activated and deactivated on every focus-gained/-lost event. The overlay's own commands are private to it (no other part registers a competing handler for them), so registering on the workbench-level IHandlerService is sufficient to keep them reliably reachable, regardless of how the target editor's own context nesting behaves.

The shortcut-hint tooltip still depends on which context is currently active (not on handler activation, which is now permanent), so it continues to be recomputed on every focus transition, exactly as before — just through a single, generic hint-refresh step instead of being interleaved with handler (de)activation.

Out of scope for this change: suppression of the target editor's native text-widget shortcuts (Ctrl+Z/C/V/X/A, arrow keys, etc., so that they act on the overlay's input fields rather than the editor) continues to rely on the existing reflective setActionActivation/global-action-handler mechanism, unchanged. Replacing that reflection-based workaround is intentionally left to a follow-up (see below) to keep this change focused and reviewable.

Builds upon

This is the next step in a series of incremental refactorings of the Find/Replace overlay's command handling:

• Find/Replace overlay: decouple toggle button state from action execution #4164 — decouple toggle button state from action execution
• Find/Replace overlay: unify action responsibility in FindReplaceOverlayAction #4169 — unify action responsibility in FindReplaceOverlayAction
• Find/replace: centralize UI state notifications in FindReplaceLogic #4176 — centralize UI state notifications in FindReplaceLogic
• Find/replace: add test for whole-word availability with unavailable regex #4178 — add test for whole-word availability with unavailable regex
• Find/Replace overlay: separate command infrastructure into dedicated class #4184 — separate command infrastructure into a dedicated class
• Find/replace overlay: move action management to command class #4185 — move action management to the command class

Follow-ups

This change is itself a stepping stone. Planned follow-ups building on the same command-infrastructure foundation:

• Replace the reflective setActionActivation/global-action-handler suppression of the target editor's native shortcuts with a proper, non-reflective mechanism built on the same handler/expression infrastructure introduced here.
• Decouple FindReplaceOverlay from StatusTextEditor, so the overlay can be used with other kinds of targets.

How to test

Manually:

1. Open an editor, invoke Find/Replace (Ctrl+F) to open the overlay.
2. Open Preferences > General > Keys and filter for "Find and Replace" — the overlay's commands (search forward/backward, replace, toggle options, close, ...) should be listed and rebindable.
3. Rebind one of them (e.g. "Find and Replace: Search Forward") to a different key, apply, and confirm the new shortcut works while the search field has focus, and that the button's tooltip reflects the new binding.
4. Confirm shortcut hints in the button tooltips only show up for the bar that currently has focus: focus the search field and hover over a replace-only button (and vice versa after opening the replace bar) — no stale/incorrect hint should be shown.
5. Confirm Ctrl+F while the overlay has focus closes the overlay rather than opening a duplicate dialog.
6. Confirm native text editing shortcuts (Ctrl+Z/C/V/X/A, arrow keys, Home/End, etc.) still operate on the overlay's search/replace fields rather than the underlying editor.

Automated: the existing FindReplaceOverlayTest suite (org.eclipse.ui.workbench.texteditor.tests) exercises the overlay's search/replace/history/option behavior and passes unchanged.

Screenshot

State of Work

I will still give this PR some polishment and probably extract out some further preparatory changes in addition to the ones already mentioned above before submitting this PR. I still wanted to provide it as draft for making aware of this work and for early testing/feedback already.

[github-actions]

Test Results

   855 files  ±0     855 suites  ±0   51m 49s ⏱️ - 13m 59s
 8 119 tests ±0   7 874 ✅  - 2  243 💤 ±0  2 ❌ +2 
20 259 runs  ±0  19 599 ✅  - 6  654 💤 ±0  6 ❌ +6 

For more details on these failures, see this check.

Results for commit 4933ee0. ± Comparison against base commit c3e5d57.