Include property and event return types in RequiredNamespaceCollector

[ElektroKill]

Link to issue(s) this covers:
#2842

Problem

The ZennoLab.Structures.Properties.Resources class contained a property that had it's return type set to System.Globalization.CultureInfo but the accessor parameters used System.Object. This caused the RequiredNamespaceCollector not to detect the System.Globalization namespace. This led to the assertion mentioned in the issue.

Solution

Include return types of properties and events in the analysis done by RequiredNamespaceCollector.

fixes #2842

[siegfriedpammer]

Thank you for your contribution!