DocFx annotations should not use line numbers to reference code snippets

[ghost]

Some of the C# code snippets used in the DocFX markdown are referenced by line number. As discovered in #3711, it is easy to break the documentation when the structure of the referenced code is changed. In parallel with #4169, I'm hoping to resolve the following under issues:

• Review all line number based code snippets to ensure they are correct
• Refactor DocFX all line references across .md and .cs files to use #region references
• Add checks on the build system to warn or fail if line number references are used

Links

• DocFX Code Snippet
• Helper C# Program (needs work)
• See also (Improvements for the docs  #3492)

[Aaronontheweb]

Add checks on the build system to warn or fail if line number references are used

I am very excited about that.