Move BinderObserver-related handling to BinderObserver

In IPCThradState:
 - extract the BinderObserver-related handling into a single wrapper
   function
 - move the tracking logic to BinderObserver::onBeginTransaction and
   BinderObserver::onEndTransaction.
 - move the construction and unregistering of the stats queue to
   BinderObserver so

This is to make it easier to guard the logic by runtime config.

Bug: 299356196
Test: atest binderUnitTest
Flag: build.RELEASE_LIBBINDER_BINDER_OBSERVER
Change-Id: I11e9b4b64f6d38a20b1b9c17f99c4203e23aa5f9