Add some missing JNI string functions, GetObjectArrayElement, and all the primitive array region functions.

This also pulls the UTF-8/UTF-16 functions out of class String.

Change-Id: I75936b84fd619c9cf91f6e6a6037488220b05781
diff --git a/build/Android.common.mk b/build/Android.common.mk
index 306e8e3..f13fdd0 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -69,6 +69,7 @@
 	src/stringpiece.cc \
 	src/stringprintf.cc \
 	src/thread.cc \
+	src/utf.cc \
 	src/utils.cc \
 	src/zip_archive.cc