Unified Diff: Keep/Undo actions missing icons in REPLACE_MODE

[tobiasmelcher]

Problem

When using `UnifiedDiffMode.REPLACE_MODE`, the Keep and Undo actions shown in the inline diff toolbar are rendered as plain text labels without icons. In other unified diff modes, icons are used for these actions consistently.

Screenshot

Expected Behavior

The Keep and Undo actions in `REPLACE_MODE` should display icons, consistent with the other modes.