Using reflection to add handler for user preference events (dotnet/corefx#37853)

Using reflection to add handler for user preference events (dotnet/corefx#37853)

* using reflection to add handler for user preference events

* adding comments, correcting typo and using GetType

* adding debug.asserts

* pushing down color translator

* using open unbound delegate pointing directly to getter method of the eventargs category property

* No longer using colorTable on netcoreapp 2.1 in system.Drawing.Common

* reverting the use of extension method.

* doing  s_color check first and adding null check for category getter

* missing semicolon

* improving comments and adding tests

* removing extra using

* using already defined known color

* skipping the test on nano and non-windows platform

* introducing a custom property

Commit migrated from https://github.com/dotnet/corefx/commit/d24b3e33e66bfd0733f9c01fa810336d76a8872f