ART: Convert pointer size to enum

Move away from size_t to dedicated enum (class).

Bug: 30373134
Bug: 30419309
Test: m test-art-host
Change-Id: Id453c330f1065012e7d4f9fc24ac477cc9bb9269
diff --git a/runtime/mirror/string.h b/runtime/mirror/string.h
index e2cfb8d..d492ba3 100644
--- a/runtime/mirror/string.h
+++ b/runtime/mirror/string.h
@@ -35,7 +35,7 @@
 class MANAGED String FINAL : public Object {
  public:
   // Size of java.lang.String.class.
-  static uint32_t ClassSize(size_t pointer_size);
+  static uint32_t ClassSize(PointerSize pointer_size);
 
   // Size of an instance of java.lang.String not including its value array.
   static constexpr uint32_t InstanceSize() {