dex_cache: rewrite StringDexCachePair as DexCachePair<T>

.. with [T = mirror::String]. This is in preparation for introducing
a dex cache array for MethodTypes, which will be treated the same way.

Test: make test-art-host
bug: 30550796
Change-Id: Ief4455b4c6e4c9dd897f2c40b14b843a57b1dc8e
diff --git a/runtime/class_linker-inl.h b/runtime/class_linker-inl.h
index d5b3090..51e5aae 100644
--- a/runtime/class_linker-inl.h
+++ b/runtime/class_linker-inl.h
@@ -67,9 +67,9 @@
   // MethodVerifier refuses methods with string_idx out of bounds.
   DCHECK_LT(string_idx, declaring_class->GetDexFile().NumStringIds());;
   mirror::String* string =
-        mirror::StringDexCachePair::LookupString(declaring_class->GetDexCacheStrings(),
-                                                 string_idx,
-                                                 mirror::DexCache::kDexCacheStringCacheSize).Read();
+        mirror::StringDexCachePair::Lookup(declaring_class->GetDexCacheStrings(),
+                                           string_idx,
+                                           mirror::DexCache::kDexCacheStringCacheSize).Read();
   Thread::PoisonObjectPointersIfDebug();
   if (UNLIKELY(string == nullptr)) {
     StackHandleScope<1> hs(Thread::Current());