Does not compile against Avalonia 11.0.0-preview4

[hez2010]

The constructor of KeyEventArgs had been made internal since 11.0.0-preview4 so AvaloniaEdit now failed to build.

[Numpsy]

fwiw, I've tried building it against the Avalonia 11 nightly builds, and I don't see this issue any more, but there are a bunch of other places that have been broken by the removal of interfaces in AvaloniaUI/Avalonia#9553 and also few uses of ReadOnlySlice that seems to have been removed

[danipen]

@Gillibald

[Gillibald]

We are about to merge some breaking changes to Avalonia itself. After that is done I will adjust AvaloniaEdit so you will be able to use latest nightly builds.

[danipen]

Thanks 🙏

[chenjing1294]

Avalonia 11.0.0-preview5 release

[danipen]

The project was updated to 11.0.0-preview5: #305