Bug 1854009 - wasm: Use load32 for loading subtyping depth. r=bvisness

The subtyping depth field on STV is 32-bits, we should use load32.

The hardcoded subtyping depth limit and LEB byte order currently
save us here, but we shouldn't rely on that.

Differential Revision: https://phabricator.services.mozilla.com/D188643

js/src/wasm/WasmFrameIter.cpp

@@ -723,7 +723,7 @@ void wasm::GenerateFunctionPrologue(MacroAssembler& masm,
           // Load the subtyping depth of the expected function type. Re-use the
           // index register, as it's no longer needed.
           Register subTypingDepth = WasmTableCallIndexReg;
-          masm.load8ZeroExtend(
+          masm.load32(
               Address(WasmTableCallSigReg,
                       int32_t(SuperTypeVector::offsetOfSubTypingDepth())),
               subTypingDepth);