microsoft/compiler: Handle input coverage

Note that GL requires input coverage for sample execution mode to
be only the single bit corresponding to the executing sample, so
rearrange things to understand during shader emitting if we're
executing per-sample to emit the right coverage value.

Reviewed-by: Sil Vilerino <sivileri@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14624>
3 files changed