gallium: add pipe cap for scissored clears and pass scissor state to clear() hook

gallium: add pipe cap for scissored clears and pass scissor state to clear() hook

this adds a new pipe cap that drivers can support which enables passing buffer
clears with scissor test enabled through to be handled by the driver instead
of having mesa draw a quad

also adjust all existing clear() hooks to have the new parameter

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4310>