[WindowDecor] Skip hover animation if task is not in focus.

This CL makes it so that if the task is not in focus (on top), hovering
over the maximize button will not show the hover animation, which in
turn will not show the maximize menu at the end of the animation.
However, clicking the maximize menu should still bring the task to
front and maximize the task.
In addition, if we get a relayout call while the hover is in progress
but the task has lost focus, we explicitly cancel the hover, since we
don't get a HOVER_EXIT signal if a new task launching on top blocks the
hover.

The implementation uses the taskInfo's isFocused rather than the global
focus because the former is per-display, so hovering over the top task
in each display should still show the hover animation and maximize menu.

Bug: 394939272
Test: atest DesktopModeWindowDecorationTests
Flag: EXEMPT bug fix
Change-Id: Ibbfe821f79e6843696757d1acf39457cb19dafc7