[Introspection] Introspection tests should check the enum values when possible.

Following issue https://github.com/xamarin/xamarin-macios/issues/15445 we found out that the reason for the bug was a developer doing the bind wrongly and re-ordering the enum in alphabetical order. This might have been done in several places, meaning that we have more than one enum wrong.

Introspection should be able to catch this type of issues.

Start by locating the introspection tests and reviewing issue 15445 for the enum-binding failure that motivated this request. Determine how enum values are currently represented and checked, then define a testable approach that catches incorrectly reordered enum values wherever possible.

Written by the indexing model from the issue text.