Generate better error message for incompatible **kwargs

This output is from #8772:

$ mypy test.py 
test.py:6: error: Argument 2 to "dumps" has incompatible type "**Dict[str, int]"; expected "bool"
test.py:6: error: Argument 2 to "dumps" has incompatible type "**Dict[str, int]"; expected "Optional[Type[JSONEncoder]]"
test.py:6: error: Argument 2 to "dumps" has incompatible type "**Dict[str, int]"; expected "Optional[Tuple[str, str]]"
test.py:6: error: Argument 2 to "dumps" has incompatible type "**Dict[str, int]"; expected "Optional[Callable[[Any], Any]]"
Found 4 errors in 1 file (checked 1 source file)

The error messages are pretty confusing. We should special case this and produce a customized error message that explains the situation better.

Here's the code that triggers the errors:

import json

json_kwargs = dict(indent=2)

json.dumps({}, **json_kwargs)

Some ideas about what to do:

• Generate a single error message instead of multiple ones.
• Add a note suggesting the use of Dict[str, Any] or a TypedDict type for the **kwargs argument.
• Maybe also explain that mypy matches the value type against all arguments, or add a link to documentation (add something to common issues, for example).

まず、test.py の例を json.dumps で再現し、#8772 の出力と比較します。既存の **kwargs のエラー報告を追跡し、その結果を Dict[str, Any] または TypedDict についてのガイダンスを含む、単一の明確な診断にします。混乱を招く重複したエラーがなくなったことを確認します。