Allow ImageFormatter#== to factor width and height

What does this MR do?

This change allows two Gitlab::Diff::Positions to be considered not equal when their image position width or height properties are different.

It enables a new GraphQL mutation !24027 (merged) to be able to update just a DiffNote's position.width or position.height properties.

Previously, a change to just the width or height would not be assigned within Notes::UpdateService, as DiffNote#position=(new_position) did not assign new_position when formatter was considered the same and the formatter only compared x and y properties of the position when assessing this.

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