[analyzer] Introduce "event" mechanism in CheckerManager.

A checker can register as receiver/listener of "events" (basically it registers a callback
with a function getting called with an argument of the event type) and other checkers can
register as "dispatchers" and can pass an event object to all the listeners.
This allows cooperation amongst checkers but with very loose coupling.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126658 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed