Putting icon on link label baseline as good as possible cross-browser
and unify code with Vector skin's code. With one improvement,
putting icon in `:before` selector in order to be able to specifically
change icon independent from link, which opens up `opacity` or state
changes.
Also cleaning up CSS by
- reducing specificity
- changing to `stylelint-disable-line` only on specific selectors
- removing initial value `transparent`
Bug: T207075
Change-Id: Ib5d446434263441eb85aa2e96a0e4dbde1034c1c
Depends-on: I92acb9851a3c0acdbc40a4a4528a91c7332c9293
f6e5d24941