Use the schema package's Markdown parser and walk its AST to extract
examples.
These changes also rename StripNonRelevantExamples to FilterExamples.
This is preparatory work for #4159 and #4632.
In particular, use the parser to filter and extract examples. This also
sets up support for entity references in documentation that can be used
in order to render language-specific names for resources, functions,
types, and properties.
Related to #4632 and #4159.
* Add a new template for examples section. Extract the examples section into a structured format for custom template processing.
* Update the description IFF we were able to extract examples sections from it.
* Update doc comments and add missing file header for the newly added file.
* Make the example description readable. Add a check for empty example sections.
* Add a chooser right below the Example Usage header. Remove javascript as a language.
* Allow an empty new-line between short-codes boundaries.
* Add tests for the examples processing.
* Update the schema-based code generators to strip out non-relevant code examples wrapped in short-codes.
* Extract language relevant examples for Functions too.
* Simpler way of extracting the surrounding text from the description.
* Add some more new-line characters to clean-up the examples sections.
