3.2.0: back out changes to Path Item Object and bring its $ref field back

[ralfhandl]

Fixes#3734 by

• adding $ref field back to Path Item Object
• removing Reference Object as an alternative to Path Item Object in four places

Builds on and includes

• 3.2.0: sync with 3.1.1 #4066

[mikekistler]

Looks good. 👍

[handrews]

@ralfhandl I'll look at this once the "built on" stack is resolved :-)

[ralfhandl]

I'll look at this once the "built on" stack is resolved

In case you are curious, these are the changes: ralfhandl/OpenAPI-Specification@3.2.0-sync-with-3.1.1...3.2.0-back-out-changes-to-path-item-object

• bring back $ref field in Path Item Object
• remove Reference Object as an alternative to Path Item Object in four places

[handrews]

@ralfhandl if we follow the proposal in #3677 (comment), we will not need this PR as we will just abandon v3.2.0-dev in favor of a reconstructed v3.2-dev, where the reconstruction just omits the commits that made this change that we want to back out.

[ralfhandl]

@handrews Thanks for taking over!