Enable DocumentationAnalyzers for build and live analysis.

• Add package reference to DotNetAnalyzers/DocumentationAnalyzers.
• Disable all rules

Rule documentation:
https://github.com/DotNetAnalyzers/DocumentationAnalyzers/blob/master/docs/StyleRules.md
https://github.com/DotNetAnalyzers/DocumentationAnalyzers/blob/master/docs/PortabilityRules.md
https://github.com/DotNetAnalyzers/DocumentationAnalyzers/blob/master/docs/Refactorings.md

For example, #14220 fixed DOC104: UseSeeLangword rule violations.