[RFC] Migrate to AvaloniaUI

Is your feature request related to a problem? Please describe.
Right now we have editor only for win platform.
For going crossplat we need to migrate to avalonia or maui
MAUI dosen't fits bc support for linux provide community and not MS devs.

Describe the solution you'd like
MVVM Crossplat RxUI Stride.Editor.

Describe alternatives you've considered
There is also MVU approach but in MVU we CAN'T easily replace views if we need and it will make editor plugins & customization harder to develop.
On the other side MVU MUCH simplier then MVVM.
However, even with all the pros and cons, I tend to favor slightly more development time and flexibility than ease and complexity of extensibility.

Additional context
dunno

Here are some questions that can aid in the description of the feature request:

• What are the usecases?
  Stride.Editor on MacOS and Linux

• What kind of options/settings are expected/wanted?
  All what we have in editor RN. we need to made few platform specific services also

• What would the (pseudo) code look like?
  Well...

• Is the feature affecting behaviour in the editor?
  50/50. It adds crossplat support. But common behaviour must be same as now

• Is there a component or datastructure?
  MVVM or MVU. We need to choose solution that will suite for us. Also if we pick MVVM we can write plugins in MVVM/MVU approach

• what kind of documentation is needed or needs to be updated?
  dunno

• Should there be an example project?
  no

Related Open Collective Project
https://opencollective.com/stride3d/projects/editor-rewrite-avalonia

The issue provides no file or test entry point; start by mapping the existing Windows-only Stride.Editor and its platform-specific services. Compare the Avalonia and MAUI constraints described here, then define the MVVM/RxUI migration boundary and completion criteria for matching current editor behavior on macOS and Linux.