Better handling of alias

Description

We want to provide better handling of alias:

• Alias to primtive type
• Alias to map
• Alias to Array
• Alias of Alias

for the following components/scopes:

• requestBody
• parameters in the operation
• model properites
• response

openapi-generator version

Latest master

Related issues/PRs

Suggest a fix/enhancement

As a starting point, we've filed https://github.com/OpenAPITools/openapi-generator/pull/360. Please expect more PRs to come.