UX improvements for inline code quality [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This MR handles UX feedback for the inline code quality icons/annotations feature (#2526 (closed)) introduced by !57926 (merged). This MR adds a white border to the inline code quality icons to allow for proper contrast with the background no matter which code theme they appear in, and this MR adds a modal to open when an inline code quality icon is clicked that displays the details of the new violations on that line.

Testing instructions:

• This is a GitLab Ultimate feature, defined as inline_codequality in license.rb so you must have the appropriate license loaded to see the feature
• This feature is behind the feature flag :codequality_mr_diff_annotations - echo "Feature.enable(:codequality_mr_diff_annotations)" | rails c to enable it
• The default code quality template is designed for docker-in-docker, but I would recommend setting up a specific local runner using these instructions if you want to fully test this in your gdk

Screenshots

gutter icons in diff view	tooltip on hover	modal on click

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?) Not needed because this is behind a feature flag
• I have added/updated documentation, or it's not needed. (Is documentation required?) Not needed because this is behind a feature flag
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.