fix: Add in gizmos on assembly load

[Eideren]

PR Details

User-defined gizmos did not load in when reloading the assembly, whether they were part of the previous version or not.
Same deal for DisplayAttribute stuff, also cleaned up registered types when assemblies are unloaded, and replaced the unreadable linq into someting more readable

Related Issue

None afaict.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.