Replace ACE with Editor Lite

What does this MR do?

Replaces ACE editor for merge request conflict resolution with Editor Lite.

⚠ Note that his MR depends on two other MRs:

• !46251 (merged). [Download patch]
• !46283 (merged). [Download patch]

So if you would like to perform a click-test you need the patches for these two MRs as well.

Screenshots (strongly suggested)

Before (ACE)	After (Editor Lite)
ScreenFlow	ScreenFlow1

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

Related to #273016 (closed)