[baseline][arm64] Generate Sbfx instead of (Asr; Sxtw) when Untagging Smi values.

Very small change to the arm64 macro assembler.
This improves Preact by 0.8% on a Neoverse-N1 machine.

Change-Id: I867e73eb9b999e6f74fd54d72c6bf3f139d3b62f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3833819
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82522}

src/codegen/arm64/macro-assembler-arm64-inl.h

@@ -1065,8 +1065,7 @@ void TurboAssembler::SmiUntag(Register dst, Register src) {
   }
   DCHECK(SmiValuesAre32Bits() || SmiValuesAre31Bits());
   if (COMPRESS_POINTERS_BOOL) {
-    Asr(dst.W(), src.W(), kSmiShift);
-    Sxtw(dst, dst);
+    Sbfx(dst, src.W(), kSmiShift, kSmiValueSize);
   } else {
     Asr(dst, src, kSmiShift);
   }