Content-Type application/json;charset=UTF-8 is not serialized/deserialized as JSON

[tnaumann-wecg]

Jane version(s) affected: 7.5.4

Description
If a JSON content type is including a charset suffix like application/json;charset=UTF-8, it is not serialized or deserialzed (depending on if it is present in request or response body schema) to/from JSON.

How to reproduce

openapi: 3.0.3
info:
  title: content-type-reproducer
  version: v1
servers:
  - url: https://api.example.com
paths:
  /post/data:
    post:
      operationId: operation
      requestBody:
        content:
          application/json;charset=UTF-8:
            schema:
              type: object
              properties:
                prop:
                  type: string
      responses:
        200:
          description: success
          content:
            application/json;charset=UTF-8:
              schema:
                type: object
                properties:
                  prop2:
                    type: string

The generated Endpoint will neither encode the request body to JSON (leading to a Type Error when passing the body data to StreamFactory::createStream) nor decode a JSON response to object.

Possible Solution
It seems like a similar bug was fixed in #115. I managed to hack a workaround by modifying RequestBodyGenerator, to only check the content type string before the ; character against the registered generators.
If this sounds like a legit approach I'd be willing to submit a PR containing this fix.