Provide the full parsed config file to each plugin

Feature

Provide the full parsed config file to each plugin

Pitch

Currently, Mypy plugins are passed only the Options object in their constructor, which captures Mypy options but not Mypy plugin options. Consequently, each plugins has to re-parse the file. This is a waste of time, may add to the necessary dependencies for a plugin with configuration, and requires re-implementing the logic for parsing different file types (TOML vs config). Here's an example of the pydantic plugin doing just this:

https://github.com/pydantic/pydantic/blob/06448aa41764d0c1e1c2f9455b108c4b21012929/pydantic/v1/mypy.py#L239-L256

The neatest solution would be to pass the full config object to the constructor. Unfortunately, this would be a breaking change to the constructor signature, so probably the more palatable option would be to store the config options within each Plugin instance (in the constructor), which the subclasses can use if they want:

class SomeMypyPlugin(Plugin):
    def __init__(self, options: Options) -> None:
        super().__init__(options)
        my_config_option = self.raw_config["tools"]["some_mypy_plugin"]
        # use my_config_option

Plugin コンストラクターと設定読み込みパスから始め、次に issue にリンクされている pydantic plugin の例と比較します。現在 Options と plugin の設定がどのように解析されているかを追跡し、各 plugin が TOML または設定ファイルを再解析しなくても、解析済みの設定全体を plugin インスタンスから利用できる状態を完了と定義します。