Convert Commit dropdown to Vue

What does this MR do?

• Converts the commit options dropdown to Vue/pajamas.
• Removes Browse files from becoming part of dropdown in mobile displays and leaves it as a button full-width.
• Removes the dropdown section divider when not needed.

Test locally(GDK)

Go to any commit and observe the options dropdown. Fixes styling when user not logged in.

Screenshots (strongly suggested)

platform	before	after
desktop
mobile
desktop
mobile

When user not logged in(fixed divider showing)

before	after

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• 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 #299346