Pull Request Description

This PR implements a basic type hierarchy of parent relations to allow the searcher to suggest completions for compatible types. This only works for self types as doing it for return types would require implementing proper type checking logic.

Closes #1445.

Important Notes

N/A

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the Scala, Java, and Rust style guides.
• All documentation and configuration conforms to the markdown and YAML style guides.
• All code has been tested where possible.