Remove the `run` method from `OpPassManager` and `Pass` and migrate it to `OpToOpPassAdaptor`

This makes OpPassManager more of a "container" of passes and not responsible to drive the execution.
As such we also make it constructible publicly, which will allow to build arbitrary pipeline decoupled from the execution. We'll make use of this facility to expose "dynamic pipeline" in the future.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D86391