Cache FunctionDescriptor Category property

[bendikberg]

Purpose

The Category property of the FunctionDescriptor potentially calls .GetName on every assembly every time it is accessed, and this takes a lot of time during workspace loading. By caching the category, this price of accessing the assemblies is only paid once.

There might be issues if the assemblies are reloaded, but the FunctionDescriptor is not?

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated
• This PR contains no files larger than 50 MB

Release Notes

N/A

Reviewers

@mjkkirschner

FYIs

@dimven