[mlir] Add operations to BlockAndValueMapping and rename it to IRMapping

The patch adds operations to `BlockAndValueMapping` and renames it to `IRMapping`. When operations are cloned, old operations are mapped to the cloned operations. This allows mapping from an operation to a cloned operation. Example:

```
Operation *opWithRegion = ...
Operation *opInsideRegion = &opWithRegion->front().front();

IRMapping map
Operation *newOpWithRegion = opWithRegion->clone(map);
Operation *newOpInsideRegion = map.lookupOrNull(opInsideRegion);
```

Migration instructions:
All includes to `mlir/IR/BlockAndValueMapping.h` should be replaced with `mlir/IR/IRMapping.h`. All uses of `BlockAndValueMapping` need to be renamed to `IRMapping`.

Reviewed By: rriddle, mehdi_amini

Differential Revision: https://reviews.llvm.org/D139665