Port System.Drawing.Printing.MarginsConverter (dotnet/corefx#33640)

Port System.Drawing.Printing.MarginsConverter (dotnet/corefx#33640)

* Exposes System.Drawing.Printing.MarginsConverter

Adds tests for MarginsConverter

Fixes dotnet/corefx#33441

* sort usings

* - nit fixes
- whitespace formatting
- code cleanup

* Fix formatting

* Moves MarginsConverter to System.Windows.Extensions

* Add missing using statement and remove extra line

* Apply PR feedback, undo caching.

* Fixing test failures on netfx

* Add comments and put mono headers

* Replace source code with referencesource content

* Cleanup

* Removing SuppressMessage Attributes

* Keeps FullFramework condition to show subtle differences

* Remove duplication

* Updating test and keeping fullframework code for CreateInstance

Commit migrated from https://github.com/dotnet/corefx/commit/a53d140654fe049036b9e9faee05371ebb6cdcb4