fix: Add and test missing mobile Bys

[TroyWalshProf]

Change list

Add missing MobileBy.ClassName and TagName

Types of changes

What types of changes are you proposing/introducing to .NET client?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New feature (non-breaking change which adds value to the project)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Documentation

• Have you proposed a file change/ PR with appium to update documentation?

This can be done by navigating to the documentation section on http://appium.io selecting the appropriate command/endpoint and clicking the 'Edit this doc' link to update the C# example

Integration tests

• Have you provided integration tests to pass against the beta version of appium? (for Bugfix or New feature)

Details

Add missing implementations of MobileBy ClassName and TagName

[TroyWalshProf]

@akinsolb - Ready for review

[laolubenson]

Does it?