Use symlinks in the build graph for jni libs

Now that ninja uses lstat and can support installing arbitrary symlinks,
switch jni lib symlinks from LOCAL_POST_INSTALL_CMDS to real rules.

Bug: 128577186
Test: List of files under PRODUCT_OUT is the same before/after this change
Test: out/target/product/generic/.installable_files now includes the symlinks
Test: m installclean; m NfcNci -> symlinks installed with correct dest
Test: m NfcNci; m NfcNci -> ninja: no work to do
Change-Id: I078dca53ab3d93f74c36fa66d5577e6e3e0640d6