Apexd: Hook up postinstall code

In the new flow, Postinstall should be performed when a session is
being scanned and staged.

Refactor the code and expose an additional binder function so that
apexservice_test can "unit-test" postinstall.

Bug: 119260955
Bug: 120799580
Test: atest apexservice_test
Change-Id: I534b68015df1208e6983b9f4a7a2c38e235891d0
11 files changed
tree: 19ef56642cf7237fd1fe6fb579e9094cf16e1e30
  1. apexd/
  2. apexer/
  3. proto/
  4. tests/
  5. OWNERS
  6. PREUPLOAD.cfg