Add support for features in JetBrains

[sestinj]

The majority of features in VS Code are also implemented in JetBrains, but there are currently a few that are not. If you have any questions about what these mean, or are interested in making a PR, please reach out!

Larger un-implemented features:

• codebase indexing, @ codebase and @ folder context providers
• tab-autocomplete

Minor un-implemented features:

• @ diff context provider
• @ open files context provider "pinned" option
• @ terminal context provider
• @ search context provider
• @ problems context provider
• @ locals (debugger) context provider