nir/lower_tex: Make the adding a 0 LOD to nir_op_tex in the VS optional.

This controls the whole lowering of "make tex ops with implicit
derivatives on non-implicit-derivative stages be tex ops with an explicit
lod of 0 instead", but it's really hard to describe that in a git commit
summary.

All existing callers get it added except:
- nir_to_tgsi which didn't want it.
- nouveau, which didn't want it (fixes regressions in shadowcube and
  shadow2darray with NIR, since the shading languages don't expose txl of
  those sampler types and thus it's not supported in HW)
- optional lowering passes in mesa/st (lower_rect, YUV lowering, etc)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16156>

src/broadcom/compiler/vir.c

@@ -613,6 +613,7 @@ v3d_lower_nir(struct v3d_compile *c)
                 .lower_txp = ~0,
                 /* Apply swizzles to all samplers. */
                 .swizzle_result = ~0,
+                .lower_invalid_implicit_lod = true,
         };
 
         /* Lower the format swizzle and (for 32-bit returns)