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/filetests/filetests/verifier/bitcast.clif

@@ -10,14 +10,14 @@ block0(v0: i32):
 ; bitcast to a type larger than the operand is not ok
 function %valid_bitcast2(i32) -> i64 {
 block0(v0: i32):
-    v1 = bitcast.i64 v0 ; error: The bitcast argument v0 has a lane type of 32 bits, which doesn't match an expected type of 64 bits
+    v1 = bitcast.i64 v0 ; error: The bitcast argument v0 has a type of 32 bits, which doesn't match an expected type of 64 bits
     return v1
 }
 
 ; bitcast to a smaller type is not ok
 function %bad_bitcast(i64) -> i32 {
 block0(v0: i64):
-    v1 = bitcast.i32 v0 ; error: The bitcast argument v0 has a lane type of 64 bits, which doesn't match an expected type of 32 bits
+    v1 = bitcast.i32 v0 ; error: The bitcast argument v0 has a type of 64 bits, which doesn't match an expected type of 32 bits
     return v1
 }