Value types were previously represented internally as either enum values for "basic," i.e. non-reference, non-tuple types or pointers to `TypeInfo` structs encoding either references or tuples. Update the representation of reference types to use one bit to encode nullability and the rest of the bits to encode the referenced heap type. This allows canonical reference types to be created with a single logical or rather than by taking a lock on a global type store and doing a hash map lookup to canonicalize. This change is a massive performance improvement and dramatically improves how performance scales with threads because the removed lock was highly contended. Even with a single core, the performance of an O3 optimization pipeline on a WasmGC module improves by 6%. With 8 cores, the improvement increases to 29% and with all 128 threads on my machine, the improvement reaches 46%. The full new encoding of types is as follows: - If the type ID is within the range of the basic types, the type is the corresponding basic type. - Otherwise, if bit 0 is set, the type is a tuple and the rest of the bits are a canonical pointer to the tuple. - Otherwise, the type is a reference type. Bit 1 determines the nullability and the rest of the bits encode the heap type. Also update the encodings of basic heap types so they no longer use the low two bits to avoid conflicts with the use of those bits in the encoding of types.