[RISCV] RISCV vector calling convention (2/2) (#79096)
This commit handles vector arguments/return for function definition/call,
the new class RVVArgDispatcher is added for doing all vector register
assignment including mask types, data types as well as tuple types.
It precomputes the register number for each argument as per
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#standard-vector-calling-convention-variant
and it's passed to calling convention function to handle all vector arguments.
Depends on: #78550
