add ndk atrace sample

Native tracing sample is non-trivial as mentioned here: https://developer.android.com/topic/performance/tracing/custom-events#native-code

and would be a useful kickstart sample

Start by reading the linked Android documentation on custom native tracing events, especially the native-code section. Use the existing ndk-samples structure as the entry point, then add a self-contained atrace sample that demonstrates native tracing as a kickstart; the issue does not name a specific file or test to run.

Written by the indexing model from the issue text.