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/memory_region.h b/runtime/memory_region.h
index fbb0441..f018c1f 100644
--- a/runtime/memory_region.h
+++ b/runtime/memory_region.h
@@ -178,9 +178,9 @@
   }
 
   // Is `address` aligned on a machine word?
-  template<typename T> static bool IsWordAligned(const T* address) {
+  template<typename T> static constexpr bool IsWordAligned(const T* address) {
     // Word alignment in bytes.
-    size_t kWordAlignment = GetInstructionSetPointerSize(kRuntimeISA);
+    size_t kWordAlignment = static_cast<size_t>(GetInstructionSetPointerSize(kRuntimeISA));
     return IsAlignedParam(address, kWordAlignment);
   }