Only show the code navigation areas when hovering over a line
Increase width of the popover
Allow the popover to be scrolled veritcally
Show 'this is the definition' text instead of a button
for areas which are the current definition

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/213190, https://gitlab.com/gitlab-org/gitlab/-/issues/218586, https://gitlab.com/gitlab-org/gitlab/-/issues/213188