APIs and misc support for tags

[karenetheridge]

Support searching for tags, and for the subfields within tags, including x- properties.

[karenetheridge]

and also

OAI/OpenAPI-Specification#4063

OAI/OpenAPI-Specification#4356

new fields added for 3.2.

[karenetheridge]

• when returning a match in $options, include all its tags as well as metadata like parent, kind etc that comes from global (document-relative) data
• when processing a document, search for duplicate tags, circular heirarchies, etc.