Automatic disambiguation of file extensions

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> As described in https://github.com/microsoft/vscode/issues/129004#issuecomment-882751887, I don't feel the current behaviour file association is effective in VSC for full-stack or versatile programmers. There is prior art in the form of [`neel1996/langline`](https://github.com/neel1996/langline) although the heuristics implementation didn't really inspire @TylerLeonhardt. That package uses GitHub Linguist which is highly tested but relies on hardcoded regexes.. as seen in https://github.com/github/linguist/blob/617fa486aad61043996e1323a429c900493c89a7/lib/linguist/heuristics.yml#L30 and other files. The Tensorflow ML approach would be much more versatile than the Github Linguist NPM module, and other staff members mentioned using that for disambiguation. However, Linguist IDs would need to be matched to their corresponding `languageId`. The ML would also need to be trained to recognise contributed language(s). Also noting: > I also think there are different heuristics that would be better like looking at what other files are in the workspace and see what their modes are.