[Managed.Windows.Forms] Revert a revert commit that accidentally changed the wrong code

When the commit 8334fe3a56c978ffe7f8cb199536f9b3234afdbe was reverted in a791cfc1640bec442757f78fe71e428d643e90ed, accidentally the wrong chunk of code was changed.

This commit reverts the changes correctly.
[Managed.Windows.Forms] Added more asserts to the CurrencyManagerTest2 test

These were useful while investigating 4b50211fb7f1dd2621673edd100f30eb39098d7d