ExpressionParser ctor in 1.5.0 not compatible with earlier versions

[Matthias-Meyer]

In 1.5.0, an optional parameter usedForOrderBy was added to the System.Linq.Dynamic.Core.Parser.ExpressionParser ctor. Since optional parameters are evaluated at compile time, this version is not compatible with older versions.
This is now a problem because we all want to upgrade to 1.6.1 with the vulnerability fixed, but need to wait for all dependent projects to compile their code and upgrade their package references.
I'd say it would be better to add a 2nd ctor with an extra non-optional parameter.

[StefH]

#882