[pm] refactor to extract more installation logic

Next step is to extrat all installation related logic to something like
"InstallationCoordinator". Then we have a clear view of what is holding
the locks and how to encapsulate them inside PackageManagerService.

BUG: 194319951
Test: builds
Change-Id: Id14d1cb7d0bd122d37bfaceef630e2361e74cd3c