[llvm] [WebAssembly] Implement lowering calls through funcref to call_ref when available (PR #162227)

[Demetrius Kanios via llvm-commits]

QuantumSegfault wrote:

> Since you are adding a new instruction I think we also need MC tests that cover assembling them, (like the tests in test/llvm/MC/WebAssembly) so we can cover things like encodings of instructions (and e.g. check out the tests that cover use of __indirect_function table).

Oh, I didn't know. I was following the pattern of, again, https://github.com/llvm/llvm-project/pull/147486

I'll look into writing an appropriate test. Should I also test `ref.test` while I'm at it, since that one also lacks a MC test?

https://github.com/llvm/llvm-project/pull/162227