glsl/lower_precision: Lower builtins depending on arguments

glsl/lower_precision: Lower builtins depending on arguments

When an ir_call is encountered that invokes a builtin, it will now try
to generate a lowered version of the builtin. This only happens if all
of the arguments to the function are lowerable. Previously the builtin
would be inlined before the lowering pass is invoked and then the
implementation would be lowered as a consequence of the pass. However
this causes problems if the builtin has multiple arguments and the
implementation has operations on only a few of the arguments before
combining it with the others. In that case the entire builtin should
only be lowered if all of the arguments are lower precision. The
previous approach would end up lowering only parts of the
implementation.

The lowered implementations are cached in a hash table in case they can
be reused.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3885>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3885>