Merge raw_bitcast and bitcast (#5175)

- Allow bitcast for vectors with differing lane widths
- Remove raw_bitcast IR instruction
- Change all users of raw_bitcast to bitcast
- Implement support for no-op bitcast cases across backends

This implements the second step of the plan outlined here:
https://github.com/bytecodealliance/wasmtime/issues/4566#issuecomment-1234819394

cranelift/codegen/src/isa/riscv64/lower.isle

@@ -814,11 +814,6 @@
    (lower (has_type out (bitcast v @ (value_type in_ty))))
    (gen_moves v in_ty out))
 
-;;;;;  Rules for `raw_bitcast`;;;;;;;;;
-(rule
-   (lower (has_type out (raw_bitcast v @ (value_type in_ty))))
-   (gen_moves v in_ty out))
-
 ;;;;;  Rules for `ceil`;;;;;;;;;
 (rule 
   (lower (has_type ty (ceil x)))