Do not validate nullable annotations when targeting net472

The code base currently uses `!` suppression to avoid nullable warnings.
Rather than littering the code with `!` the nullability analysis should be disabled for net472 targets in projects that multi-target.

Alternatively, calls to APIs like `string.IsNullOrEmpty` that are annotated on net10 but not on net472 should be changed to null-annotated equivalents.

The editorconfig suppresses `IDE0370: Suppression is unnecessary` to allow unnecessary `!` when not targeting net472.
This should be removed.