This commit moves the rendering of the button back to the server, and
shows/hides it using opacity rather than display. It also removes the
transform applied to the button on hover (scale). Previously, both of these
factors automatically triggered a reflow, which creates a performance
bottleneck on pages with larger DOM size.

MR: !12103

re-apply MR !6285 "Added forceLoad ability to singleFileDiffs, added callback to getContentHTML, added conditional force load if a collapsed diff line anchor is found"

Use url utility to retrieve hash

temporarily revert "Added forceLoad ability to singleFileDiffs, added callback to getContentHTML, added conditional force load if a collapsed diff line anchor is found"

This reverts commit d2ee3808.

Vue2 was taking the template out & then appending again. This changes that

Added forceLoad ability to singleFileDiffs, added callback to getContentHTML, added conditional force load if a collapsed diff line anchor is found

Use url utility to retrieve hash

Fixed styling bugs