glsl,nir: Move i/umulExtended lowering to NIR.

glsl,nir: Move i/umulExtended lowering to NIR.

NIR already has the necessary lowering, and the GLSL lowering violates
GLSL IR validation rules.  Once quadop lowering was turned off, the IR
validation at the end of the compile path on DEBUG builds caught the
problem.

In order to move the lowering to NIR, though, we need to make sure that
drivers supporting these functions actually have the lowering flag set.

xfails added for t860, where apparently this tickles a variety of existing
64-bit bugs in the backend.

Fixes: #6461
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Mykhailo Skorokhodov <mykhailo.skorokhodov@globallogic.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16437>