Resolve "Web IDE: Discarding changes on re-named entries"

What does this MR do?

Previously in the Web IDE, when a file was changes and renamed, discarding did not discard the changes immediately. This MR updates the disacrdFileChanges action to also discard the changes when a file is renamed.

Screenshots

Before	In this MR (2020-01-07)
20200107_webide_discard_renamed_file_current	20200107_ide_discard_renamed_fix

Known issues

• Discarding a renamed directory blows up. #195776 (closed)
• The discard all feature does not behave as consistently as discarding a single file. This will be fixed in the follow up MR: !22572 (merged)
• Discarding a staged change blows up. (Issue will be created soon)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

References

• #31859 (closed)