Add support for code actions #1
Description
LSP supports code actions. CodeMirror supports diagnostic actions. These are similar, but not the same.
CodeMirror actions are attached onto the diagnostic.
LSP code actions are requested on a range and receive all related diagnostics which overlap with that range. Also these code actions can be incomplete, in which case they need to be resolved. The title is always available though.
We should find a way to make this compatible. Quick thought: When getting validations, perform a code action lookup for every diagnostic. Resolve the code action when invoked.