Fix tabbing of form fields in projects/new flow

What does this MR do?

Fixes a bug that caused weird behavior while tabbing through the form fields in the projects/new flow.

• Adjusts a CSS property which was causing a purposefully hidden select2 element to be displayed
• Removes the tabindex attribute as it caused the field to be indexed last on the page
• Adds some CSS to better indicate when the select2 box has been successfully tabbed to (when it has focus)

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

Addresses #214921 (closed)