autodect Map<String, ComplexType> from `additionalProperties`

extracted from on openapi-processor/openapi-processor-spring/issues/150

if #10 works and produces maintainable code try to automatically detect a Map<String, ComplexType> from additionalProperties without an explicit mapping:

# ...
type: object
additionalProperties:
  type: array
  items:
    type: string

or even more complex:

additionalProperties may contain an object that should be generated:

# ...
type: object
additionalProperties:
  type: object
  properties:
    foo:
      type: string
    bar:
      type: array
      items:
        type: string

首先阅读 issue #10，并追踪 additionalProperties 当前在 openapi-processor-base 中的映射方式。使用此 issue 中的两个 schema 作为案例：完成的标准是无需显式映射即可自动检测 Map<String, ...>，包括生成的嵌套对象类型。