Add updateImageDiffNote mutation

What does this MR do?

This adds the ability to update a DiffNote's position data through GraphQL (for DiffNotes that were created on an image diff).

The mutation is called updateImageDiffNote to mirror the existing GraphQL mutation createImageDiffNote. This MR refactors the existing updateNote mutation to be organised in the same way that the Notes::Create mutations are organized, to inherit from a new Base class that it shares with updateImageDiffNote.

Issue: #34353 (closed)

Screenshots

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.
• [-] Tested in all supported browsers