intelliSense completion for documentation sections

[cgranade]

Is your feature request related to a problem? Please describe. When writing documentation comments, sections like /// # Summary and /// # Description occur nearly universally, leading to a lot of additional typing required, and introducing more possibility for typos to break documentation.

Describe the solution you'd like It would be helpful if intelliSense could suggest documentation sections for autocompletion, including named subsections for inputs under the /// Input and suggesting fully-qualified names as entries in /// # See Also sections.