[SPIRV] support capabilities and extensions

This patch supports SPIR-V capabilities and extensions. In addition,
it inserts decorations related to MIFlags and improves support of switches.
Five tests are included to demonstrate the improvement.

Differential Revision: https://reviews.llvm.org/D131221



Co-authored-by: Aleksandr Bezzubikov <zuban32s@gmail.com>
Co-authored-by: Michal Paszkowski <michal.paszkowski@outlook.com>
Co-authored-by: Andrey Tretyakov <andrey1.tretyakov@intel.com>
Co-authored-by: Konrad Trifunovic <konrad.trifunovic@intel.com>