Improve & fix the performance bar UI and behavior

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2349

What does this MR do?

Improve & fix the performance bar UI and behavior

- The bar is now placed at the bottom the page
- Modals are wider
- RBlineprof modal is now using Bootstrap modal
- RBlineprof (ugly) dropdown has been replaced with clean links
- JS behavior has been improved to handle toggle if slected profiling
  has already been performed, not reloading the page in that case
- Don't show the performance bar shortcut if the feature is disabled

Screenshots

The bar

SQL queries profile modal

Line profile modal

What are the relevant issue numbers?

Closes #33910 (closed), #33914 (closed), #33909 (closed).