[WebAssembly][GlobalISel] Migrate to extended LLT (#193047)
Moves Wasm GISel to use the the new extended LLTs added by #155107.
Extended LLTs have (optional) information about whether a particular
scalar is integer vs floating-point. This is a big win for Wasm, since
we can avoid a lot of guess work, and map LLT i32, i64, f32, and f64
directly to their Wasm counterparts.
To take full advantage of this, RegBankSelect has been automated,
iterating over all operands and mapping typed LLTs to their appropriate
register bank.