Move JniConstants to points of use

Removes the JniConstants from the libnativehelper API.

Most of the constants are moved into libcore.

Light tidying up in touched files.

Bug: 119840313
Test: atest libnativehelper/test
Test: atest CtsLibcoreTestCases
Test: art/test.py --host -g -j16
Test: device boots

Change-Id: I4c0daab450d2efd7e6bd7705e27dbb6309fcb92d
diff --git a/Android.bp b/Android.bp
index bd9f278..e6b2916 100644
--- a/Android.bp
+++ b/Android.bp
@@ -37,8 +37,8 @@
     srcs: [
         "JNIHelp.cpp",
         "JniConstants.cpp",
-        "toStringArray.cpp",
         "JniInvocation.cpp",
+        "toStringArray.cpp",
     ],
 
     target: {