Reorganize public type definitions

[ybiquitous]

Because it is unclear whether a type definition is public or internal and so available from Stylelint plugin packages, there is a problem in that we cannot safely refactor type definitions.

There are a few ways to limit the publicity of type definitions:

1. Add the @internal JSDoc annotation and a warning message like this:
   

   stylelint/types/stylelint/index.d.ts

   Lines 539 to 544 in 11acf31

   	/**
   	* Internal use only. Do not use or rely on this type. It may change at
   	* any time.
   	* @internal
   	*/
   	export type InternalApi = {

2. Add a _ prefix to types or type members like this:
   

   stylelint/types/stylelint/index.d.ts

   Lines 544 to 550 in 11acf31

   	export type InternalApi = {
   	_options: LinterOptions & { cwd: string };
   	_extendExplorer: ReturnType<typeof cosmiconfig>;
   	_specifiedConfigCache: Map<Config, Promise<CosmiconfigResult>>;
   	_postcssResultCache: Map<string, PostCSS.Result>;
   	_fileCache: FileCache;
   	};

3. Remove export from internal types as possible. This way is smarter, but it may need to remove namespace:
   

   stylelint/types/stylelint/index.d.ts

   Line 6 in 11acf31

   namespace stylelint {

I believe we need to reorganize type definitions by combining such ways well.
I'm happy to hear any feedback.

Ref:

• Refactor the internal API #6415 (comment)
• Change type names to be more consistent #6503 (comment)
• The TypeScript Declaration Files

[jeddy3]

You're probably the most familiar with our types than anyone else 😄 Do you have a preference for how to combine the approaches? We can roll into v15 so that it can be a breaking change.

[ybiquitous]

@jeddy3 Thank you for your feedback. Since I may be just in time for v15, I've opened PR #6510.

[jeddy3]

Done in #6510