[Feature Request]: Support TypedDict hint in Apache Beam.

### What would you like to happen?

CoGroupByKey produces Dict[K, Union[...]], which is narrower than TypedDict. If the user follows the CoGroupByKey with a ParDo where the function takes TypeDict as input, e.g. `ParDo(fn(element: TypedDict))`, then the type check in Beam fails.

Users having types like:

```
myTypeDict = TypedDict(
'myTypeDict', {
'field_1': List[Field1Type],
'field_2': List[Field2Type],
})
```

are using less specific hints like `myLessSpecificDict = Dict(str, Union[List[Field1Type], List[Field2Type]])` in order to satisfy beams typing.

We could have a first-class typehint TypeDict, which may be easier once we deprecate Python 3.7.

### Issue Priority

Priority: 3 (nice-to-have improvement)

### Issue Components

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