[clang] [DO NOT MERGE][clang][RISCV] Introduce OFP8(E4M3, E5M2) RISC-V vector types (PR #191349)

[Brandon Wu via cfe-commits]

4vtomat wrote:

> Do we have C++ name mangling tests for RVV types? The ones I could find are for rvv-vector-bits.

I also can't find one, let me add one for ofp8 and fill out other rvv types in another PR 😂

https://github.com/llvm/llvm-project/pull/191349