Make MR diff file filter input Clear button functional

What does this MR do?

This MR makes clear button of MR diff file filter functional again where clicking the button would clear the input.

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides

Closes #51092 (closed)