[RISC-V] ELT Profiler Bring-Up (#91313)

[RISC-V] ELT Profiler Bring-Up (#91313)

* [RISC-V] Generate profiling function callbacks

Initial implementation based on ARM64 code.

* [RISC-V] Fix asm stub for calling profiler callbacks

* Fix argument registers according to RISC-V calling convention
* Fix field offsets for PROFILE_PLATFORM_SPECIFIC_DATA
* Make sure field offsets for PROFILE_PLATFORM_SPECIFIC_DATA stay fixed by static asserting the offsets in asmconstants.h

* [RISC-V] Pass arguments for Profile(Enter|Leave|Tailcall)Naked stubs in t0 and t1 because t2 is used to store the call address of the stub

* [RISC-V] Remove unimplemented definition of EmitRet

* [RISC-V] Copy struct from registers into a buffer so that profiler can see whole struct arguments laid out in memory

* [RISC-V] Implement ProfileArgIterator::GetReturnBufferAddr()

Since the RISC-V ABI says values are returned like the first named argument, re-use the struct copying routine from argument parsing as much as possible.

* Factor out duplicated test results checking routine in SlowPathELTProfiler::Shutdown()

* [RISC-V] Clean up PROFILE_PLATFORM_SPECIFIC_DATA

* Remove unused t0 field
* Remove 'unused' field and widen 'flags' to 64 bits to maintain alignment and shave off one sw instruction

* [RISC-V] Remove commented out code

* [RISC-V] Fix formatting

* [RISC-V] Apply format patch from failed check

* [RISC-V] Post-review fixes