Update IVideoCompositor example and remarks code blocks

[United600]

This pull request improves the documentation for implementing a custom video compositor by adding proper code block formatting to C# examples. This makes the examples clearer and easier to read for developers.

Documentation improvements:

• Added C# code block formatting to the example showing how to use a PropertySet and create a MediaOverlayLayer, improving readability. [1] [2]
• Added C# code block formatting to the full example implementation of a custom video compositor class, ensuring the code is properly displayed.