Implement the initial pass management functionality.

The definitions of derived passes have now changed and passes must adhere to the following:

* Inherit from a CRTP base class FunctionPass/ModulePass.
   - This class provides several necessary utilities for the transformation:
       . Access to the IR unit being transformed (getFunction/getModule)
       . Various utilities for pass identification and registration.

* Provide a 'PassResult runOn(Function|Module)()' method to transform the IR.
   - This replaces the runOn* functions from before.

This patch also introduces the notion of the PassManager. This allows for simplified construction of pass pipelines and acts as the sole interface for executing passes. This is important as FunctionPass will no longer have a 'runOnModule' method.

PiperOrigin-RevId: 235952008