Update MR widget Squash commits

Issue #17613 (closed)

MR	Changes
Part 1 > !33099 (merged)	BE implementation
Part 2 > !33827 (merged)	FE implementation of squash option and MR form
👉 Part 3 > (current)	FE implementation of squash option in MR widget
Part 4 > !35081 (merged)	FE implementation of squash option tooltip
Part 5 > !35111 (merged)	FE implementation of squash option message in MR form
Part 6 > !35392 (merged)	Additional spec for testing edge case for part 2
Docs > !33930 (merged)	Documentation

What does this MR do?

This update the MR widget squash commits to display the correct squash options selected in the Project and Merge request setting.

Testing Case

This is hidden behind a feature flag, docs

rails c

Feature.enable(:squash_options)

1. Go to a Merge Request

• The Squash commits will have the following behaviour:

Project Setting	MR Setting	MR widget Expectation
Do not allow	hidden	hidden
Do not allow	hidden	hidden
Require	Checked	Disabled, checked
Require	Unchecked	Disabled, checked
Allow	Checked	Enabled, Checked
Allow	Unchecked	Enabled, Unchecked
Encourage	Checked	Enabled, Checked
Encourage	Unchecked	Enabled, Unchecked

Setup

To set the project setting:

• Go to the Settings > General page > expand Merge requests

To set the MR setting:

• You can set the MR setting either in a New Merge Request OR you can Edit an existing Merge Request:

Note: if Do not allow is selected, the squash option will be hidden.

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
• 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

Closes #223032 (closed)