Move android.graphics JNI & APEX files into HWUI

The graphics JNI code is now separate from libandroid_runtime
and it along with HWUI headers are no longer visible to targets
outside the boundary of what is to become the UI mainline module

The exposed headers to targets outside the module are now restriced
to C APIs contained in the apex header directory.

Bug: 137655431
Test: CtsUiRenderingTestCases
Change-Id: I30d34055b6870dc1039f190a88f4a747cee17300