Tech debt: Do not expose ILanguageServerExtensionManager outside of the languageServer module #18946
Description
See discussion on https://github.com/microsoft/vscode-python/pull/18884/files#r852332963: ILanguageServerExtensionManager doesn't need to be exposed outside of language server-related classes, however at the moment everything in src/client/languageServer/types.ts can be used anywhere.