[llvm] [WebAssembly][GlobalISel] Add legalization & selection of most integer ops (PR #190234)

[Demetrius Kanios via llvm-commits]

QuantumSegfault wrote:

Okay, take 3. I was able to move most of the tests to LLVM IR. There are some cases that still require gMIR, and I've kept those
- `G_ROTR` and `G_ROTL`; there's no direct mapping from LLVM IR (and none that work without combiners). Those remain in gMIR
- Similar situation with `G_ANYEXT`; kept `anyext.mir` to be able to perform explicit checks
- All the shifts (`ashr`, `lshr`, `shl`, `fshl`, `fshr`) support shift amounts of a different type than the value in gMIR, but not in LLVM IR. I've kept those edge cases in gMIR, but moved the bulk of it to LLVM IR.
- Likewise, `cttz`, `ctpop`, and `ctlz` allow result types to differ from input. Same as shifts, moved the common cases to IR, and left MIR for the unusual ones.

https://github.com/llvm/llvm-project/pull/190234