The intent of the code base was to be run with overflow checking disabled.  However the actual settings were quite a bit different:

- CSharp: checking enabled in debug, disabled in release
- VB: checking disabled in all modes

For both languages individual projects could, and often did, override this setting.  Typically it specified the global default but not always.

This is confusing and makes it difficult to reason about our source code.  Furthermore much of our testing occurs in debug mode and it's not logical for our code to behave substantially different in Debug than it would in Release.

This change clarifies our overflow checking behavior.  It's disabled in all modes now.  The change goes further to prevent individual projects from overriding this setting and adds unit tests to make sure it was applied correctly.

Note: this PR is not intended to state whether it's better for overflow checking to be enabled or disabled.  It is intended to enforce the decision the code base was designed around.