OpenAPI 3.0.x: Schema Object `items` lint rules

[char0n]

There are specific rules around Schema Object.items rules defined by OpenAPI 3.0.x specification. The goal of this issue is to provide new linting rules aligned with the specification.

items field should be parsed as generic ArrayElement as OpenAPI 3.0.x forbids it to be an array. This is guaranteed by already existing tests and one additional introduced in #2480

Refs CC-28867
Refs CC-27491
Refs SWOS-129