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/field.cc b/runtime/mirror/field.cc
index ff6847c..65f6b16 100644
--- a/runtime/mirror/field.cc
+++ b/runtime/mirror/field.cc
@@ -68,7 +68,7 @@
     }
   }
   mirror::DexCache* const dex_cache = declaring_class->GetDexCache();
-  ArtField* const art_field = dex_cache->GetResolvedField(GetDexFieldIndex(), sizeof(void*));
+  ArtField* const art_field = dex_cache->GetResolvedField(GetDexFieldIndex(), kRuntimePointerSize);
   CHECK(art_field != nullptr);
   CHECK_EQ(declaring_class, art_field->GetDeclaringClass());
   return art_field;