This change makes `RewriterBase` symmetric to `OpBuilder`.

```
  OpBuilder           OpBuilder::Listener
      ^                        ^
      |                        |
RewriterBase        RewriterBase::Listener
```

* Clients can listen to IR modifications with `RewriterBase::Listener`.
* `RewriterBase` no longer inherits from `OpBuilder::Listener`.
* Only a single listener can be registered at the moment (same as `OpBuilder`).

RFC: https://discourse.llvm.org/t/rfc-listeners-for-rewriterbase/68198

Differential Revision: https://reviews.llvm.org/D143339