nir: fix packing of TCS varyings not read by the TES

nir: fix packing of TCS varyings not read by the TES

Unlike other stages TCS outputs not read by the TES cannot always
be demoted to globals e.g. when they are read by other TCS
invocations.

We were not taking these outputs into account when packing which
could result in other outputs being assigned to the same location.

Here we make sure to gather information on these outputs and group
them together when packing.

This fixes rendering issues in QUBE 2 via Proton.

Closes: #2653
Fixes: 26aa460940f6 ("nir: rewrite varying component packing")
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4328>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4328>