intel/compiler/fs: Switch liveness analysis to IR analysis framework

intel/compiler/fs: Switch liveness analysis to IR analysis framework

This involves wrapping fs_live_variables in a BRW_ANALYSIS object and
hooking it up to invalidate_analysis() so it's properly invalidated.
Seems like a lot of churn but it's fairly straightforward.  The
fs_visitor invalidate_ and calculate_live_intervals() methods are no
longer necessary after this change.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4012>