Avalonia 12.0 cleanup list

[kekekeks]

Tracking issue for API changes in the distant future, can be safely ignored until mid-2024

• Mark IGeometryContext as [NotClientImplementable], make sure it's used everywhere instead of StreamGeometryContext (for V11 we'll probably need IGeometryContextEx for new members)
• extend ILockedFramebuffer with alpha format
• Make TextProperties.LineSpacing public abstract Introduce TextBlock.LineSpacing #13243
• Geometry.Combine() Incorrect Parameter Type #14369
• Inconsistent List Usage in APIs #11286

[MrJul]

• Change Inline.TextDecorations from a StyledProperty to an AttachedProperty

[robloo]

This is a possibility

• Rename some Gesture events #13237

cc @workgroupengineering

[maxkatz6]

Shape.StrokeDashArray should be of IList type, instead of AvaloniaList.
This way we could reduce compositor subscriptions count by checking if stroke dash array implements INotifyCollectionChanged or not.

Right now, having AvaloniaList, code like `StrokeDashArray="10 5" will always require us to subscribe to the list changes.

[workgroupengineering]

Make DevToolsOptions a record and change the property setter in init.

[maxkatz6]

Ideally, this #4443 should be revisited as well.
Even better if ContextMenu was removed from the main assembly.

[robloo]

protected virtual string? GetHelpTextCore();
should be
protected abstract string? GetHelpTextCore();

See: #17030 (comment)