GenAPI event declaration pattern is too verbose

[MichaelSimons]

With the latest version of GenAPI, the event declaration pattern changed to be more verbose.

Before (From running GenAPI on system.codedom,8.0.0):

        public event EventHandler PopulateImplementationTypes { add { } remove { } }

After:

        public event EventHandler PopulateImplementationTypes {
            add { }
            remove { }
        }

This verbose pattern seems inconsistent with the other changes I noticed which make the declarations more compact and reduce the number of lines.

I noticed this in dotnet/source-build-reference-packages#1247 which is where the changes from #46425 flow in.

[MichaelSimons]

cc @carlossanlop, @ViktorHofer

[carlossanlop]

This one is surprising because I made sure to add tests for ApiDiff to ensure these were single lines. Unsure why it's not doing the same for GenAPI. We're probably missing similar tests for GenAPI.