Symbols for libs in APEXes are available

The unstripped file for libraries in APEXes are available via
out/target/product/<device>/symbols/apex/<apex_name>/path_to_lib.

This change make the symbol files available by installing the individual
files in APEXes to the directory where the APEXes will be mounted at
(i.e. runtime directory which is /apex/<apex_name>). Note that the files
are not actually packaged to a filesystem image; they are installed just
to create the symbol files under the out directory where developers can
use them for debugging.

Bug: 120846816
Test: m com.android.runtime.debug
There are unstripped files under
out/target/product/walleye/symbols/apex/com.android.runtime.debug

Change-Id: Ib182e2bf8787b7669ccba13814491db35370f468