Generate DXIL Shader hash

DXIL shader bitcode is hashed and the hash is placed into the final
output object file in its own data part.

This change modifies the DXContainerGlobals pass to compute the shader
hash (just an MD5 of the bitcode) and put the shader hash data into a
global for the HASH part.

This also sets the hash flag as appropriate for if the hashed shader
contained debug information. There is additional handling required to
get debug information in shaders working correctly with our tooling,
but that will be addressed in subsequent patches.

Reviewed By: python3kgae

Differential Revision: https://reviews.llvm.org/D139357