Collect element extracting from matrix into vector extracting

For example, the following SPIR-V code

```llvm
[[mat:%\d+]] = OpLoad %mat2v4float %mat9
[[mat00:%\d+]] = OpCompositeExtract %float [[mat]] 0 0
[[mat01:%\d+]] = OpCompositeExtract %float [[mat]] 0 1
[[mat02:%\d+]] = OpCompositeExtract %float [[mat]] 0 2
[[mat03:%\d+]] = OpCompositeExtract %float [[mat]] 0 3
[[cc:%\d+]] = OpCompositeConstruct %v4float [[mat00]] [[mat01]] [[mat02]] [[mat03]]
```

Can be turned into
```llvm
[[mat:%\d+]] = OpLoad %mat2v4float %mat9
[[cc:%\d+]] = OpCompositeExtract %v4float [[mat]] 0
```