[liftoff][arm64] Use 64 bit offset reg in mem op

Accessing the Wasm memory with a 64 bit offset was truncated to 32 bit,
which is fine if we check bounds first, but not if we rely on the
trap handler to catch the OOB.

R=clemensb@chromium.org

Bug: v8:11587
Change-Id: I82a3a2906e55d9d640c30e770a5c93532e3a442c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2808942Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73829}

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -128,7 +128,7 @@ inline MemOperand GetMemOp(LiftoffAssembler* assm,
                            UseScratchRegisterScope* temps, Register addr,
                            Register offset, T offset_imm) {
   if (offset.is_valid()) {
-    if (offset_imm == 0) return MemOperand(addr.X(), offset.W(), UXTW);
+    if (offset_imm == 0) return MemOperand(addr.X(), offset.X());
     Register tmp = temps->AcquireX();
     DCHECK_GE(kMaxUInt32, offset_imm);
     assm->Add(tmp, offset.X(), offset_imm);