Sweep for old/poor reference source framework links

[guardrex]

Where were a few 6.0-era ref source links that we needed to 🔪 on a PR. It's a good idea to sweep the repo and make sure that when we're linking ref source (and especially pegging to a version) that we're required to do so by the text and that we do so in the best way, including trying to link to the main branch with our ref source INCLUDES file.

This is a low-priority, long-range item to address, and it will probably be best to work it as an EOY task during the holidays ⛄. I'm going to track this via the Blazor.Docs project and assign it to a main doc set sprint later, since I don't know which month it will land in for work.