fix(oas3): fix getting initial values for request body in OpenAPI 3.x

[glowcloud]

Changes the behaviour from only getting initial values for the parameters that have examples or have type object to getting initial values for every parameter. Also fixes the issues of not getting examples and correct input in the form for anyOf and oneOf, and of not filling initial values if they are falsy. Changes based on findings documented in #9754.

Applies to request bodies with content type application/x-www-form-urlencoded and multipart/....

Before:

After:

[glowcloud]

Perhaps we could move handling these below this line

  let initialValue = fn.getSampleSchema(schema, false, {
    includeWriteOnly: true
  })

So that if the parent schema has an example, we would get the initial value from it. We would need to reassign the schema, type, format and description then.

[glowcloud]

I think $$ref should be the exception when checking if we have properties other than anyOf or oneOf in the schema.

Not sure if there's a better way of doing this than filtering out these properties.

[glowcloud]

I updated the code so that we won't be overwriting existing properties in the schema with the nested schema and created an issue for not getting nested schema properties: #9763

I'm wondering though, wouldn't this be solved by merging the nested schema with the parent schema?