Add File Review implementation to Diffs app

What does this MR do?

For #17531 (closed)

• Adds a localStorage integration in the Diffs app that loads any existing reviews for the current MR.
• Adds a event listener that will mark a given file as reviewed

Notably, this does not enable the feature in the UI.
Enabling this feature, and the associated feature flags and documentation, are in a future MR.

Timeline

Merge Request	Description
!49173 (merged) !49174 (merged) !49190 (merged) !49208 (merged)	Various cleanup merge requests in preparation for this feature.
!49506 (merged)	Identify diff files using the content_sha
!50022 (merged)	Switch identification to use blob.id
We're here 👉🏻	Add tooling to add/remove reviews from LocalStorage to accommodate the file review feature
Non-blocking detour	Add the current merge request IID to the file ID
	Add UI to review files

Screenshots (strongly suggested)

N/A, these additions are all backing code, with no UI yet.

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
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team