Add logging of dynamic loading of native code.

This uses the SELinux audit messages generated when an untrusted app,
targeting SDK 28 or lower, executes native code from an app data
directory. "Executes" here covers memory mapping a file with execute
permission (including using dl_open) or calling execve.

As with dynamic loading of DEX code we write a hash of the contents of
the file executed to the event log.

The existing unit and integration tests are extended to verify the new
behaviour.

Bug: 111338677
Test: atest -p services/core/java/com/android/server/pm/dex

Change-Id: Ifbb3b338135db413be2cd83b1a8e7499d61d88dd