Global Search - Project Filter

What does this MR do?

Part 2 of 2 for #262060 (closed)
Fixes #281037 (closed)

This change replaces the deprecated jQuery Dropdown for the Project Filter on Global Search. It replaces the deprecated module with a Vue component using GlDropdown from GitLab UI.

To do so we simply moved the API calls and data tracking into the Vuex store and hooked it into a Vue component.

The Group filter has already been replaced as part of !44833 (merged)

Screenshots (strongly suggested)

	before	after
Empty Query
With Group
With Project
No Group, Project Dropdown
With Group, Project Dropdown
Clear Button
Loading State

GIF

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