Make all Render overrides sealed

[Takoooooo]

What does the pull request do?

This is needed because at some point we might want to change the way built-in primitives are rasterized

Fixed issues

Fixes #10066

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0029850-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0029858-beta. (feed url: https://pkgs.dev.azure.com/AvaloniaUI/AvaloniaUI/_packaging/avalonia-all/nuget/v3/index.json) [PRBUILDID]

[tkefauver]

@Takoooooo How are subclasses supposed to override Render now? In my case I have 2 custom controls inheriting from Border and Canvas.

[gusmanb]

Same problem here, I have custom controls that inherit from Border and now they're dead...

Overriding Render is always useful, because you may want to just extend a bit what already exists, forcing developers to create a Control from scratch when there is something already done that may need just some minor changes is a very bad idea.

[tkefauver]

@gusmanb Definitely agree :(

It ended up being pretty easy for my Border control though. Its a really basic one like what you're mentioning and I got it working... just had to replace Border.Child usage with UserControl.Content.

[29654761]

This is very bad idea.
Avalonia can almost do nothing.

[timunie]

@29654761 it's a bad idea to comment on merged PRs. Open a Discussion with your specific issue und use-case described. If possible, show sample code.