undo breaking change: Add ParserOptions default ctor

[MikeStall]

Public default ctor for ParserOptions was wrongfully removed in #1292.
(see #1292 (comment). )

This is a breaking change and is causing other dlls to now throw:
System.MissingMethodException: 'Method not found: 'Void Microsoft.PowerFx.ParserOptions..ctor()'.'

According to the .net loader:

• A default ctor means no parameters.
• Whereas a default parameter is a compiler-level construct (the compiler will insert the default value at the callsite), but it's still a regular parameter for .net loader.

At least one occurence:

 	Microsoft.ProgramSynthesis.Repair.PowerFx.Context.EngineContext.EngineContext(Microsoft.PowerFx.Engine engine, Microsoft.PowerFx.ReadOnlySymbolTable globalSymboilTable, Microsoft.PowerFx.Types.FormulaType expectedType, bool isBehavior, bool checkExpectedType)	Unknown
 	Microsoft.ProgramSynthesis.Repair.PowerFx.RepairHandler.SuggestFixesAsync(Microsoft.PowerFx.Engine engine, Microsoft.PowerFx.CheckResult result, System.Threading.CancellationToken cancel)	Unknown