Automatic merge from submit-queue (batch tested with PRs 49665, 49689, 49495, 49146, 48934)
openapi: refactor into more generic structure
**What this PR does / why we need it**:
Refactor the openapi schema to be a more generic structure that can be
"visited" to get more specific types. Will be used by validation.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: #44589
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```