Cleanup String.<init> handling.

Move everything to one place (currently well_known_classes.cc, but
no strong preference) and define a macro to easily handle the list
of affected methods.

test: m test-art-host
test: m test-art-target
Change-Id: Ib8372d130d5458516a1f1ae31014afc76037fc34
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 57ae555..4dc4c20 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -4044,9 +4044,9 @@
   }
   bool HasDirectCodePtr() const { return GetCodePtrLocation() == CodePtrLocation::kCallDirect; }
 
-  int32_t GetStringInitOffset() const {
+  QuickEntrypointEnum GetStringInitEntryPoint() const {
     DCHECK(IsStringInit());
-    return dispatch_info_.method_load_data;
+    return static_cast<QuickEntrypointEnum>(dispatch_info_.method_load_data);
   }
 
   uint64_t GetMethodAddress() const {