* Non-obsoletion warnings as errors in Release.
* Add two other obsoletions related to collection expressions.
These are not present in the codebase, but may become so in the future.
* Exempt NU1903 so the project can't mysteriously stop building.
* Fix some FULL_RELEASE mistakes.
* diff fix
* Resharper caught this one. Note to self: Wire up resharper to CI in another PR.