Add support for references functionality

[scevallos]

What would you like to be added

Add support for the references functionality (i.e. find usages of an element, jump to an element's declaration, etc.) within the plugin, as outlined here: https://plugins.jetbrains.com/docs/intellij/reference-contributor.html

Why is this needed

Support for references within the plugin is arguably one of the most important aspects of proper language support, as it facilitates more rapid development.

Implementation details

The JetBrains documentation provides an overview of the implementation details.