KeyValuePairSettings : support non "assembly-qualified" typenames

[tsimbalar]

I am creating this issue as a result of comments on #1064 (comment)

For settings whose type is an interface or an abstract class, we allow to pass a value that is :

• full assembly-qualified type name of a concrete implementation (KeyValuePairSettings : support a fully qualified type name for arguments whose type is abstract #1056)
• special syntax to access a static property or field (see KeyValuePairSettings : support for static members via :: #1057)

When the containing assembly is Serilog, it is actually not necessary to add the assembly part in the fulle type name.

It would be nicer and more user-friendly to allow to omit the assembly part of the full type name when either of the following is true :

• a usingis already present in the settings
• the assembly is already loaded

This would allow to replace

• "Serilog.Tests.Support.DummyConcreteClassWithoutDefaultConstructor, Serilog.Tests" with "Serilog.Tests.Support.DummyConcreteClassWithoutDefaultConstructor"
• "NameSpace.To.ConcreteType::StaticProperty, AssemblyName" with "NameSpace.To.ConcreteType::StaticProperty"

[nblumhardt]

I'm working through open issues and closing most of those that have no activity in the past 12 months as stale. This helps us track and prioritize the issues that have the most impact.

If you believe that this issue still needs attention, please feel free to comment here. Thanks!