Special case strings in System.Linq.Enumerable.OrderBy (dotnet/corefx#42286)

Special case strings in System.Linq.Enumerable.OrderBy (dotnet/corefx#42286)

* Special case strings in OrderBy

* Style change to be more inline with code base, as per review

* Added OrderBy Culture test

* Added different culture OrderBy.ElementAt

* Make the tests Windows specific due to potential unicode ordering differences

* Made sorted result set dynamic due to different culturing sorting of different OSes

* Removed conditional

* Use of ThreadCultureChange, fixed Assert argument ordering

* Delousing...

Commit migrated from https://github.com/dotnet/corefx/commit/749fcdea9873d88c182ad94aef83290e96f95ff1