Search online documentation by API name and area

Add structured filters to the online documentation search so readers can search names of language and API items without receiving every prose mention.

Provide a simple Everything | Names search mode. Names mode should cover page/type names, keywords, methods, properties, events, constructors, global functions, and other documented members. Results should identify the kind of item and its documentation area.

Also allow the search to be limited by area, including Desktop, Web, Standard Library/Core API, Language, Studio, and Guides. This should make searches for shared names such as Button, Control, Pressed, or Open precise and predictable.