[SPIRV] Add PreLegalizer pattern matching for `cross` GL extension

> Note: the `cross` move deleted the SPIR-V intrinsic, so `Intrinsic::spv_cross`, its `selectExtInst` lowering, and the SPIR-V `cross.ll` test need to be restored first so the PreLegalizer combiner can emit the GL extension through the intrinsic.

Follow-up to #135425.

Following the cross implementation move, SPIR-V now lowers `cross` as a sequence of `extractelement`/`fmul`/`fsub`/`insertelement` instructions instead of the GL extension:
```asm
cross(x, y) ->
x0 = extractelement x, 0
x1 = extractelement x, 1
x2 = extractelement x, 2
y0 = extractelement y, 0
y1 = extractelement y, 1
y2 = extractelement y, 2
sub0 = fsub(fmul(x1, y2), fmul(y1, x2))
vec0 = insertelement(poison, sub0, 0)
sub1 = fsub(fmul(x2, y0), fmul(y2, x0))
vec1 = insertelement(vec0, sub1, 1)
sub2 = fsub(fmul(x0, y1), fmul(y0, x1))
vec2 = insertelement(vec1, sub2, 2)
```
We can pattern match this in `SPIRVCombine.td` and `SPIRVCombinerHelper.cpp` to
```llvm
insertelement(
insertelement(
insertelement(
poison,
fsub(
fmul(extractelement(x, 1), extractelement(y, 2)),
fmul(extractelement(y, 1), extractelement(x, 2))),
0),
fsub(
fmul(extractelement(x, 2), extractelement(y, 0)),
fmul(extractelement(y, 2), extractelement(x, 0))),
1),
fsub(
fmul(extractelement(x, 0), extractelement(y, 1)),
fmul(extractelement(y, 0), extractelement(x, 1))),
2)
```
which would allow us to change this sequence back into `cross(x, y)` so that SPIR-V emits the GL extension again.

Start with the deleted SPIR-V intrinsic, its selectExtInst lowering, and the SPIR-V cross.ll test, then read SPIRVCombine.td and SPIRVCombinerHelper.cpp. Verify the PreLegalizer combiner recognizes the shown extractelement/fmul/fsub/insertelement sequence, restores cross(x, y), and makes the SPIR-V test cover GL-extension emission.

Written by the indexing model from the issue text.