SERVER-14425 Fix a bug in the Lock Manager for the conversion path

The mode counts were not being maintained correctly and this was
introduced by commit 22b368a74b36896de6b164c55cd4b3b9ca562bb2.

This change also adds additional assertions to help catch such issues in
the future.
Merge remote-tracking branch 'nextdoor/master'

Conflicts:
	src/mongo/db/concurrency/lock_mgr_new.cpp
Revert "reverts 3 changes to locking"

This reverts commit cd2fc6dc0cb16f9ebd48025d7f5c94814a461a31.

Conflicts:

	src/mongo/db/concurrency/lock_mgr_new.cpp
	src/mongo/db/concurrency/lock_state.cpp