API changes for Slint 2.0

[ogoffart]

This issue is meant to contain API changes that we should consider in 2.0. We'll edit this list as we find more things to change:

Rust

• [ ] LogicalPosition::to_physical and PhysicalPosition::to_logical should take self by value. (See discussion in https://github.com/slint-ui/slint/pull/3017#discussion_r1246562249)
• [ ] slint::Window::dispatch_event() should return a Result<(), PlatformError>
• [ ] Check all public enums to make them non_exhaustive (eg: slint_interpreter::DiagnosticLevel)
• [ ] Make SoftwareRenderer::RepaintBufferType non-exhaustive
• [ ] Change WindowAdapter::update_window_properties(&self, _properties: WindowProperties<'_>) to return a Result<(), PlatformError> as it can fail (winit window resizing may produce error on wayland if immediate GL surface resizing fails)

C++

• [ ] LogicalPosition, PhysicalSize and so on should have a constructor that takes two values.

Slint

• [ ] Remove StyleMetrics.dark-color-scheme (replaced by Palette.color-scheme == ColorScheme.dark)