Remove legacy Diagnostics project

[MrJul]

What does the pull request do?

This PR removes the legacy Diagnostics (Dev Tools) project from the solution.
In the sample projects the new Accelerate Dev Tools are referenced instead.

Thanks to this removal, the DataGrid isn't needed in the core solution anymore: its submodule has been deleted.

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0060997-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[rabbitism]

Is it possible to move to a separate repo? Otherwise It's impossible to use a dev tool in offline machines because I can't login.

[maxkatz6]

@rabbitism, it is planned to move to a separate repo, yes. But it won't be maintained for long.

Is it possible to move to a separate repo? Otherwise, It's impossible to use a dev tool in offline machines because I can't login.

Typically, our business license allows for online keys without internet. At least for libraries. We need to discuss the same for DevTools/Parcel.
DevTools itself doesn't require internet connection but signed-in session renewal does.