[DirectX][NFC] Change specification of overload types and attribute in DXIL.td (#81184)

- Specify overload types of DXIL Operation as list of types instead of a
string.
- Add supported DXIL type record definitions to `DXIL.td` leveraging
`LLVMType` to avoid duplicate definitions.
 - Spell out DXIL Operation Attribute specification string.
 - Make corresponding changes to process the records in DXILEmitter.cpp