[mlir][ODS] Small fixes for ODS classes

* Introduce separate `RankedTensorOf` class. Use it as base class for `AnyRankedTensor`.
* Add C++ class specification (`::mlir::MemRefType`) to `MemRefRankOf` and `StaticShapeMemRefOf`.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D95936