Consolidated $ref-to-Some Object feature request

[handrews]

This issure consolidates and replaces the numerous "can the OAS allow $ref for..." issues:

• Security Requirement: Add security to the components object #1850
• Security Scheme: How do I refer to external securitySchema object ? #1972 (but see also Use URI references for Security Requirements in 3.2 #3776 for an alternative)
• Server: change specification to permit $ref of server objects #2338
• Tags: Allow the use of $ref and json pointer in tags #2905
• Operation: Feature Request: $ref for Operation Object  #2922 (but note that there are impacts on finding and resolving operationId)
• Media Type: Allow $ref in request body and response content objects #3056 (closed because the specific use case is handled by overriding description with a Reference Object); also Reusable media types #2845 although there is more to that one)
• Contact: [feature] support of $ref in contact fields  #3552
• License: [feature] support of $ref in licence fields #3569