Handle arrow operator (#3768)

This change implements the check behavior for the arrow operator.

`ptr->Foo()` is rewritten as `(*ptr).Foo()` and `ptr->(X.y)` is
rewritten as `(*ptr).(X.y)`

toolchain/check/pointer_dereference.cpp

@@ -0,0 +1,31 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "llvm/ADT/STLFunctionalExtras.h"
+#include "toolchain/check/context.h"
+#include "toolchain/check/convert.h"
+#include "toolchain/parse/node_ids.h"
+#include "toolchain/sem_ir/ids.h"
+
+namespace Carbon::Check {
+
+auto PerformPointerDereference(
+    Context& context, Parse::AnyPointerDeferenceExprId node_id,
+    SemIR::InstId base_id,
+    llvm::function_ref<auto(SemIR::TypeId not_pointer_type_id)->void>
+        diagnose_not_pointer) -> SemIR::InstId {
+  base_id = ConvertToValueExpr(context, base_id);
+  auto type_id =
+      context.GetUnqualifiedType(context.insts().Get(base_id).type_id());
+  auto result_type_id = SemIR::TypeId::Error;
+  if (auto pointer_type =
+          context.types().TryGetAs<SemIR::PointerType>(type_id)) {
+    result_type_id = pointer_type->pointee_id;
+  } else if (type_id != SemIR::TypeId::Error) {
+    diagnose_not_pointer(type_id);
+  }
+  return context.AddInst({node_id, SemIR::Deref{result_type_id, base_id}});
+}
+
+}  // namespace Carbon::Check