[arm64] Add missing scope around UseScratchRegisterScope.

`UseScratchRegisterScope` should be used in a block scope, to avoid keeping the
scratch register in use for longer than it's needed. Spotted when experimenting
with the `v8_enable_heap_sandbox` and `v8_enable_external_code_space` flags.

Change-Id: I34330f3e4dbd114aa75efb0ebdcf557f0bd45f11
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3256997Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/main@{#77679}

src/builtins/arm64/builtins-arm64.cc

@@ -1891,10 +1891,12 @@ static void Generate_InterpreterEnterBytecode(MacroAssembler* masm) {
   __ Ldr(kJavaScriptCallCodeStartRegister,
          MemOperand(kInterpreterDispatchTableRegister, x1));
 
-  UseScratchRegisterScope temps(masm);
-  temps.Exclude(x17);
-  __ Mov(x17, kJavaScriptCallCodeStartRegister);
-  __ Jump(x17);
+  {
+    UseScratchRegisterScope temps(masm);
+    temps.Exclude(x17);
+    __ Mov(x17, kJavaScriptCallCodeStartRegister);
+    __ Jump(x17);
+  }
 
   __ Bind(&return_from_bytecode_dispatch);
 
@@ -1932,8 +1934,12 @@ static void Generate_InterpreterEnterBytecode(MacroAssembler* masm) {
 
   __ Bind(&trampoline_loaded);
 
-  __ Add(x17, x1, Operand(interpreter_entry_return_pc_offset.value()));
-  __ Br(x17);
+  {
+    UseScratchRegisterScope temps(masm);
+    temps.Exclude(x17);
+    __ Add(x17, x1, Operand(interpreter_entry_return_pc_offset.value()));
+    __ Br(x17);
+  }
 }
 
 void Builtins::Generate_InterpreterEnterAtNextBytecode(MacroAssembler* masm) {