Unified Diff: Make overlay toolbar actions accessible via keyboard shortcuts #2938

Problem

The overlay toolbar shown in the text editor when unified diff is active provides the following actions:

• Revert
• Hide Diff
• Previous Change
• Next Change
• Open 2-way Compare Editor

These actions are currently only reachable via the mouse. There is no way to trigger them from the keyboard, which is a significant accessibility gap and a productivity issue for keyboard-centric users.

Expected Behavior

All actions provided by the unified diff overlay toolbar should be accessible via the keyboard — either through dedicated key bindings registered in the Eclipse key binding system, or via some other keyboard-accessible mechanism (e.g., command palette integration).

Acceptance Criteria

• Each overlay toolbar action has a corresponding Eclipse command with a default key binding.
• The key bindings are documented and conflict-free with existing Eclipse defaults.
• The feature works without needing to click the overlay toolbar at all.