[api-documenter] Classes should also populate Yaml type parameters

[zelliott]

Summary

This was an existing bug that was originally found when working on https://github.com/microsoft/rushstack/pull/3469 and pulled out into its own fix PR. See this thread: https://github.com/microsoft/rushstack/pull/3469#discussion_r923930778.

Details

No additional details.

How it was tested

I manually validated that YamlDocumenter._writeYamlFile writes the appropriate content. Unfortunately, the checked in .yml files don't change because of the convertUDPYamlToSDP function that strips out the newly-added typeParameter Yaml content. 🤷