Motivation

Second to last step for #1938. The only part missing is proper linearization of singleton ancestors, which I'm working on.

This PR uses the type checker introduced in #2187 to provide go to definition, hover, completion and signature help inside singleton contexts.

Implementation

I split each feature by commit:

1. Definition
2. Hover
3. Completion
4. Signature help

The only notable part of the implementation is completion. When invoking methods on a singleton, we know the receiver type, which means we can show all available methods immediately when the user types the dot.

To support that, we needed a few extra changes:

1. Started considering dot a trigger character
2. When we type in the dot, Prism will consider whatever is the next node to be name of the incomplete method call. We need to know that completion is being triggered by a dot character so that we can search for all available methods instead of trying to extract the name from the AST
3. Finally, when providing completion with the dot, the range that we're substituting in the text edit is slightly different, which we need to ensure is correct or else the editor rejects all completion candidates

Automated Tests

Added tests for all the features.

Manual Tests

Launch the LSP on this branch and start testing features for things invoked directly on singletons (remember that ancestors are still missing for now!).