Changes:
* Add a step which checks that generated code is up to date
* Copy over the documentation on how to work with `<reference>`
* Fixup a broken reference in the .sln
* Fix the casing on Microsoft.Extensions.ValueStopwatch.Sources
* Remove some unused references and variables
* Remove obsolete targets, properties, and scripts
* Replace IsProductComponent with IsShipping
* Undo bad merge to version.props
* Update documentation, and put workarounds into a common file
* Replace usages of RepositoryRoot with RepoRoot
* Remove API baselines
* Remove unnecessary restore feeds and split workarounds into two files
* Enable PR checks on all branches, and disable autocancel