Create python protos library build targets.

Change-Id: I11ec40a065a5e2892790a74dcf12b4d1dd513b5e
Test: m graph_ams; adb shell dumpsys activity --proto > activity.bin; graph_ams activity.bin > activity.dot; dot -Tpdf activity.dot -o activity.pdf
Bug: 419577469
Flag: EXEMPT build infra and tools