fixes #25605

#25605

Fixes #23484

Fixes #23621

Part of #25740

To support TS Server plugins for languages like angular, we will allow extensions to register new langauges for TypeScript to watch. The angular language for example would want ng-html files to also be uploaded to TypeScript for checking

The current language definitions all define both a set of language modes they support and a set of file extensions. The file extension part is unnessiary and may be incorrect depending on how a user sets up their `file.associations` in the workspace. This change removes the extensions part so that we always make use of the language mode

This reverts commit b9988fed.