sm: lazy service - fix race

There is a possible race:
- service registers binder A
- service registers client callback (cc1) for A
- sm send cc1 "A hasClients"
- service registers binder A (again - bad behavior!)
  - side effect: "hasClients" implicitly set to false
- service registers client callback (cc2) for A
- sm sends cc1 and cc2 "A hasClients"

Due to an intentionally overly careful check in client
callbacks, they crash when this double-send of
'hasClients' is hit.

This CL retains the state of cc1 in order to fix the
issue. Comments are added with various details about
the implementation, and b/279948722 is filed to
resolve these comments.

Bug: 279898063
Test: aidl_lazy_test
Change-Id: Ida443d5b02f19736baabdc57ff283995cdcc2a87