Fix VisualBasic.Chr method recognition

[TymurGubayev]

Fixes #1030

Problem

Any method called Chr was treated as if it was Microsoft.VisualBasic.Chr.

Solution

• Add a test case for custom methods called Chr and ChrW
• Move the check for Chr and ChrW in a separate method
• Adjust the check to not have false-positive result
• Also, in IsCultureInvariant remove the symbol name check as redundant

[GrahamTheCoder]

Thanks for this, and sorry it took me so long to get it merged!