Reuse compare editor when opening the same changed file multiple times

[Philipp0205]

Summary

When opening a changed file multiple times from the changed files view, a new compare editor tab is created each time instead of reusing the existing editor. This clutters the editor area with duplicate tabs for the same file.

Current Behavior

1. Open a pull request in the plugin
2. Navigate to the changed files view
3. Double-click or open a changed file → compare editor opens
4. Double-click the same file again → a second compare editor tab opens for the same file
5. Repeat → multiple duplicate tabs accumulate

Expected Behavior

When opening a changed file that already has an open compare editor:

• The existing editor should be brought to focus/front
• No new tab should be created
• The user should see the already-open editor instance

This matches the standard Eclipse editor behavior for regular file editors.

Motivation

• Reduces tab clutter: Users don't accumulate duplicate tabs during PR review
• Improves navigation: Users can quickly return to files they've already opened
• Consistency: Aligns with Eclipse IDE conventions where files reuse their editors
• Better UX: Reduces cognitive load and manual tab management

Acceptance Criteria

• Opening an already-open changed file brings the existing compare editor to front
• No duplicate compare editor tabs are created for the same file
• Behavior works consistently from the changed files view
• If the file content has changed (e.g., new commits), the editor updates accordingly

Technical Considerations

• Check if a compare editor is already open for the file path before creating a new one
• Use Eclipse's IWorkbenchPage.findEditor() or similar API to locate existing editors
• May need to store editor input metadata to match against opened files
• Consider how this interacts with different compare editor types (inline vs. side-by-side)

Additional Context

This enhancement improves the user experience during pull request reviews where developers frequently revisit the same files while reviewing comments or making comparisons.