Resolve "Merge request approval button style inadvertently changed"

What does this MR do?

Fixes a minor visual regression for the MR approval button. This button should appear solid when an approval is required before merging.

This also removes the use of gl-loading-icon in favor of the loading property of gl-button, which also has the side effect of preventing users from triggering the @click action when the button is in a loading state. (Previously this would trigger an error message at the top of the screen as you are trying to approve/unapprove an already approved/unapproved MR)

This addresses both #224139 (closed) and #29151 (closed)

Screenshots

button style correction:

before after
before after

loading style/behavior improvement:

before after
approve-old approve-new

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

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 #224139 (closed) and #29151 (closed)

Edited by GitLab Release Tools Bot