Port the incremental source generator polyfill code to the 6.0 servicing branch. (#72219)
* Port the incremental source generator polyfill code to the 6.0 servicing branch.
* Use common code
* Add logging extensions
* Fix typo on project Compile item and enable producing packages for both packages that need to be serviced.
* Allow ValueListBuilder to work with empty scratch spans (#70917)
Co-authored-by: Jose Perez Rodriguez <joperezr@microsoft.com>
Co-authored-by: Stephen Toub <stoub@microsoft.com>