Documentation bug: Link to debugging FUDC in non-SDK projects is dead

[Pxtl]

Visual Studio Version

NA

Summary

In https://github.com/dotnet/project-system/blob/main/docs/up-to-date-check.md there is a link to https://github.com/dotnet/project-system/blob/main/docs/fast-up-to-date-legacy.md which is a 404.

Steps to Reproduce

1. Go to https://github.com/dotnet/project-system/blob/main/docs/up-to-date-check.md
2. Click the second documentation link.

Expected Behavior

An article on FUDC for legacy-projects

Actual Behavior

404

User Impact

I had to dig up the process for managing FUDC on old non-SDK projects here:
https://github.com/dotnet/project-system/blob/b536d25b38d1a7770fb983c65c89b826f5af7a83/docs/up-to-date-check.md