Add CodeInfo to JNI methods.

It has no stack maps. We only store the frame info there.

As a consequence of having CodeInfo, the JNI methods are
now classified as IsOptimized().

This does not have any real effect on .oat file size.

Test: test-art-host-gtest
Change-Id: I8d03a3af347dc7239719bb3c39ecf84c6eaece80