Instead of defining somewhat high level mouse actions, allow granular
control of mouse clicks and mouse down/up/move events. We will want to
simulate things like holding down a mouse button after double clicking
and then dragging the mouse to another position in the future, and this
enables that.
Instead of trying to locate the relevant StyleSheetList on style element
removal from the DOM, we now simply keep a pointer to the list instead.
This fixes an issue where using attachShadow() on an element that had
a declarative shadow DOM would cause any style elements present to use
the wrong StyleSheetList when removing themselves from the tree.
Before this change, :hover wouldn't match anything outside the shadow
boundary when hovering elements inside a shadow tree. This was most
noticeable when hovering the text inside an input element and hover
styles disappearing from the hosting input element itself.
Before this change, removing a style element from inside a shadow tree
would cause it to be unregistered with the document-level list of sheets
instead of the shadow-root-level list.
This would eventually lead to a verification failure if someone tried to
update the text contents of that style element, since it was still in
the shadow-root-level list, but now with a null owner element.
Fixes a crash on https://www.swedbank.se/
