Documentation popup

[altavir]

Add a hover or Shift+Tab documentation popup on functions, classes and properties like it is done in Python.

[ileasile]

There are several steps in this issue:

1. Make the ivy resolver (or some other resolver if we decide to switch to it) resolve sources JARs. Currently they are not resolved and not downloaded.
2. Make resolved JARs to be a part of underlying module sources (add resolved JARs to module's source roots). Some new keys should be added to ScriptCompilationConfiguration to achieve this.
3. Add support for this in REPL analyzer. I hope it will not require some IDE compiler modules, but I'm not sure.
4. Finally, provide the corresponding endpoint in kernel