Extract comments from code samples of "Program structure" article to get them translated

[BartoszKlonowski]

This pull request closes #43924

For all three pages of "Program structure" article this PR goes through all code snippets and moves comments from the code to the text (embedding them or explaining if needed, so they are not left out of context).

Only the last page "Top-level statements - programs without Main methods" does not contain code that would have comments requiring translations.
The only code snippet, in the ## using directives section, was already moved in the previous page and the translated text does not relate to it.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/fundamentals/program-structure/index.md	General Structure of a C# Program
docs/csharp/fundamentals/program-structure/main-command-line.md	Main() and command-line arguments