[RISC-V] Implement emulate single step feature. (#94711)

[RISC-V] Implement emulate single step feature. (#94711)

* [RISC-V] Implement emulate single step feature.

* [RISC-V] Fix clang16 build error.

Error message  /home/clamp/runtime/src/coreclr/debug/inc/riscv64/primitives.h:52:5: error: integer value -1 is outside the valid range of values [0, 255] for this enumeration type [-Wenum-constexpr-conversion]
              (CorDebugRegister)(-1), // X0 is zero register that is not a real register. We need padding here for proper mapping with ICorDebugInfo::RegNum.
              ^

* [RISC-V] Fix sign bit.