Move libandroid_runtime headers into frameworks/base/core/jni

Move libandroid_runtime's headers into its source directory, and export
them to modules that link against libandroid_runtime.  Also fixes
one unused-paramter warning that was hidden by the use of -isystem to
include frameworks/base/include.

Bug: 33630870
Test: m -j native
Change-Id: Id6c2561d6c7d82a7ca2d183f11b1d3d3dcb42843