[MLIR][SPIRVToLLVM] SPIR-V types size in bytes function

Added `getSizeInBytes()` function as a class member to several SPIR-V types:
`ScalarType`, `ArrayType` and `VectorType`. This function aims at exposing
the functionality of `getTypeNumBytes()` from `SPIRVLowering.cpp`. Support
of more types will be added on demand.

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D83285