[mlirv][spirv] Add KHR Cooperative Matrix type and extension

Start plumbing through support for the `SPV_KHR_cooperative_matrix`
extension: https://github.com/KhronosGroup/SPIRV-Registry/blob/master/extensions/KHR/SPV_KHR_cooperative_matrix.html.

Register the extension, add new coop matrix type, and add
`spirv.KHR.CooperativeMatrixLength` op to exercise it.

Make sure that mixing of the KHR and NV coop matrix extensions is not
allowed. Make cast verification more robust.

Reviewed By: antiagainst, qedawkins

Differential Revision: https://reviews.llvm.org/D154877