Avalonia.ReactiveUI deprecated as of version 11.3.xx

[tomhornyak]

As I am building a commercial product, I do not want deprecated packages. My first change will probably upgrade to 11.3.12 and use the current package.

[tomhornyak]

In my branch I migrated to ReactiveUI.Avalonia - it was a no brainer - no changes were needed.
I also upgraded to 11.3.12 and upgraded all the other packages.
Also used the new clipboard methods and replaced the obsolete ones - getting ready for 12.x

[cuikp]

today I upgraded it from Avalonia 11.2.x to 11.3.12