WIP: Implement FE for "MR feedback" (creating an MR from a remediation)

What does this MR do?

Add split button for new vulnerability actions

• add split button that allows for the creation of an issue, creation of a merge request, or the download of a patch
• add logic to conditionally render split button with single button

Screenshots

Before

After

This state is still possible

And new state as well

Disabled

Merge Request Created!

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

Related to #216300 (closed) Related to #216651 (closed) Depends on !31142 (merged) Depends on !31498 (merged)