Remaining JSON Schema Tweaks for OAS 3.1

[philsturgeon]

With #1977 in the bag, the majority of the work for aligning JSON Schema and OpenAPI Schema Objects has been done for v3.1 (🥳).

Here is a list of remaining clarifications and "further discussions", split into individual issues to avoid overloading any one of them with an unmanageable amount of comments.

Description	Owner	Issue	Status
Clarify text relating to formats	@philsturgeon	#2093	Somebody wanna tell me some words to write?
Make clear the difference between OAS examples object and JSON Schema examples array	@darrelmiller	#2094	Unknown
$schema guidance	@philsturgeon	#2017	PR going through feedback #2266
Improve explanation of Reference Object		#388	Done
So what do we do about $ref siblings	@MikeRalphson	#2089	Done in #2181
Define the scope of $id resolution	@darrelmiller	#2092	Done
Clarify Nullable properties with default vales	@tedepstein	#2115	Done
Clarify spec wrt readOnly and writeOnly in referenced schemas	@tedepstein	#1622	Done (dropped readOnly/writeOnly definition in the OAS spec to use JSON Schema definitions instead)
v3.1 Meta Schema (Schema Object Only)	@handrews	#2016
v3.1 Meta-schema (all of OpenAPI)
Deprecate discriminator?	@tedepstein	#2143	Generally seems like a yes, but we need to be more confident in the OpenAPI Vocab direction first? So that a "simple code gen" vocab can be used to restrict some of these keywords or put discriminator back if it ever leaves.

[handrews]

Thanks, @philsturgeon.

@darrelmiller @webron while we sort these things out, keep in mind that I expect we'll publish a draft-handrews-json-schema-03 (or whatever) with clarifications and bugfixes. So we can also tweak wording and add clarifications on the JSON Schema side.

If we find something that needs it, we can also release a new meta-schema (e.g. 2020-03 or something). It's not like many implementations have caught up to 2019-09 yet, so rolling out a minor update will just mean that they'll target 2020-NN instead of 2019-09.

[handrews]

@OAI/tsc Progress on the bugfix/clarification JSON Schema draft mentioned in the previous comment can be tracked under the draft-08-patch1 milestone.

[handrews]

@philsturgeon #2016 is only a meta-schema for the schema object.
We should have a separate issue tracking a schema (not meta-schema) for the entire OAS 3.1 document.