fix(Quick Reblog): apply AlreadyReblogged colour to whole button

[AprilSylph]

Description

• fixes Quick Reblog: Reblogged status indication does not affect whole button #1923

Before	After

This PR is also a refactor of the AlreadyReblogged CSS:

• Targeting of reblog buttons has been simplified, dropping the attribute checks on the a/button in favour of relying on just the AlreadyReblogged classname on the footer and the presence of a reblog icon
• The green/purple/red color override is now applied to the entire button, making the extra CSS for colouring the tick pseudo-element redundant

Setting --icon-color-primary is not necessary to recolour icons in the new iconset, but I've kept a rule for setting that on the icons anyway, for compatibility's sake.

Testing steps

1. Load the modified addon with a blank config
2. Enable Quick Reblog
3. Use Quick Reblog to reblog a post
   • Expected result: The post's reblog icon turns green
   • Expected result: The post's reblog icon gains a green tick
   • Expected result: The reblog button's reblog count turns green
4. Use Quick Reblog to queue a post
   • Expected result: The post's reblog icon turns purple
   • Expected result: The post's reblog icon gains a purple tick
   • Expected result: The reblog button's reblog count turns purple
5. Use Quick Reblog to draft a post
   • Expected result: The post's reblog icon turns red
   • Expected result: The post's reblog icon gains a red tick
   • Expected result: The reblog button's reblog count count turns red
6. Enable Classic Footer
   • Expected result: The reblogged post(s) keep their coloured reblog icons
   • Expected result: The reblogged post(s) keep their coloured ticks
7. Disable Classic Footer's "Turn reblog buttons back into links" option
   • Expected result: No visual changes occur

Compatibility

1. Disable the postFooterSplitNotesCountSingleAction feature, and reload the page
2. Find the post(s) you reblogged with Quick Reblog previously
   • Expected result: Those posts have green reblog buttons, and green ticks
3. Use Quick Reblog to queue a post
   • Expected result: The reblog button turns purple, and gains a purple tick
4. Use Quick Reblog to draft a post
   • Expected result: The reblog button turns red, and gains a red tick

[marcustyphoon]

Doesn't work on the old, never-released postFooterSplitNotesCount footer, a fact which has a non-zero chance of eventually becoming relevant, but we can deal with that if it happens.