clutter: Avoid rounding compensation when invalidating 2D actors

clutter: Avoid rounding compensation when invalidating 2D actors

This allows the redraw clip to be more constrained, so MetaCullable doesn't
end up rendering portions of window shadows, frame and background when a
window invalidates (part of) its contents.

(cherry picked from commit a7df459416dc46321204c98197e4fd84724976e0)

Bug-Ubuntu: https://launchpad.net/bugs/1767648
Bug: https://bugzilla.gnome.org/show_bug.cgi?id=782344
Applied-upstream: 3.30.3, commit:afc91f0804ad1350fa09aa141b93020f28143b48

Gbp-Pq: Name clutter-Avoid-rounding-compensation-when-invalidating-2D-.patch