[LLDB][RISCV] Add RV64C instruction support for EmulateInstructionRISCV

Add:

- RV64C instructions sets.
- corresponding unittests.
- `c.break` code for lldb and lldb-server

Fix:
- wrong decoding of imm in `DecodeSType`

Reviewed By: DavidSpickett

Differential Revision: https://reviews.llvm.org/D136362