Add new C# code blocks to class ref pages

[paulloz]

Modified the following class ref pages:

• AStarGrid2D
• Engine
• Font
• Node
• OS
• Tween

There are a couple of workarounds in the Tween page, that'll need to be updated when Callable.Bind gets implemented.

[paulloz]

Sorry about all the CI issues, didn't realize we needed to write <> as <>. Fixed the last one, but won't push before there's an answer to that last question to not trigger another useless series of checks.

[akien-mga]

Thanks!