Bring types in from API dependency

[TonyGravagno]

In my local version of the extension, I brought in the ExplicitFoldingHub and ExplicitFoldingConfig interfaces, and made them types. All files now refer to this internal file. That's all that's required to eliminate the dependency on @zokugun/vscode.explicit-folding-api.

Would you accept a PR with this?

This would eliminate the need to publish both packages for the one extension, and would eliminate the problem that I fixed in my recent PR to the API repo.

[daiyam]

No, it's also used by https://github.com/zokugun/vscode-cobol-folding

[daiyam]

made them types

I've already made the change.