This moves us to clear on rebuild, which allows us to remove yet another place
where we track stylist dirtiness.
Bug: 1390255
Reviewed-by: heycam
MozReview-Commit-ID: nihQbUAbh8
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>
This commit also removes the old restyle_hints module and splits it into
multiple modules under components/style/invalidation/element/.
The basic approach is to walk down the tree using compound selectors as needed,
in order to do as little selector-matching as possible.
Bug: 1368240
MozReview-Commit-ID: 2YO8fKFygZI