[BUG] [R] Nested anyOf/oneOf cause the R client to generate unusable code

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

The linked spec containing an anyOf within a oneOf generates code which does not load the Foo object correctly:

> library(openapi)
> 
> foo <- Foo$new()
> foo$fromJSONString('{ "tag": "Bar", "contents": ["baz", ["x"]] }')
{
    "tag": "Bar"
}
 
> foo$contents
NULL

foo$contents should not be NULL.

openapi-generator version

6.2.1 and master branch

OpenAPI declaration file content or url

https://gist.github.com/avandecreme/c68ec04615dbc9faaaf70c6d27599a14

Generation Details

openapi-generator-cli generate -i ./openapi.json -g r -o ./generated-sdk

Steps to reproduce

Generate the api and run the example code above.

Suggest a fix

The issue comes from this generated line of code:

        self$`contents` <- ApiClient$new()$deserializeObj(this_object$`contents`, "array[AnyOfstringarray]", loadNamespace("openapi"))

array[AnyOfstringarray] is not valid.
I couldn't find how to fix that though.

Start with the linked OpenAPI spec and reproduce the issue using openapi-generator-cli generate -i ./openapi.json -g r -o ./generated-sdk. Inspect the generated R model and the ApiClient$new()$deserializeObj call for the invalid array[AnyOfstringarray] type, then verify that foo$contents loads from the sample JSON instead of remaining NULL.