Compiler fixes for ‘as’ operator

Have both “As” and “To” casting methods in PSConverter to handle differences
Moved all duplicated casting code from functions.cs into PSConverter
Made DynamicConversion handle ‘as’ casting mode
Added UpconvertOnly bool to Argument so that annoying playscript casts to bool/string don’t mess up overloading
Renamed ConvertToInt to just ToInt, renamed ConvertToObject to UntypedToObject
Added compiler tests in ConversionTest