[mlir][IR] Improve `clone` function return type of shaped types

There are `clone` overloads that take a shape as a parameter. These overloads are guaranteed to return a ranked shaped type.

`TensorType::clone`/`BaseMemRefType::clone` used to always return a `TensorType`/`BaseMemRefType`. The variants that take a shape parameter now return a `RankedTensorType`/`MemRefType`. Better static type information can make extra casts at the call site obsolete.

E.g.:
```
{TensorType/RankedTensorType} t;
t.clone({1, 2})  // now returns RankedTensorType instead of TensorType
```

Also improve documentation for `clone`.

Differential Revision: https://reviews.llvm.org/D150865