connexion: Multiple files upload (mutlipart/form-data) is ignored for Flask

Description

Consider following endpoint definition:

  /test-formData-file-upload:
    post:
      summary: 'Test formData with file type, for file upload'
      operationId: fakeapi.hello.test_formdata_file_upload
      responses:
        '200':
          description: OK
      requestBody:
        content:
          multipart/form-data:
            schema:
              x-body-name: formData
              type: object
              properties:
                formData:
                  type: array
                  items:
                    type: string
                    format: binary
              required:
                - formData

What we are doing in here is uploading multiple files from the same mulipart field. That gets correctly pulled from flask_request but ignored later in connexion.operations.abstract.AbstractOperation#_get_file_arguments

Expected behaviour

Request to Flask-based application with multiple files is correctly processed and we get multiple files available inside of handler.

Actual behaviour

Multiple files are ignored, only first is taken into account.

Steps to reproduce

1. open connexion/tests/fixtures/simple/openapi.yaml
2. find /test-formData-file-upload definition
3. Use snippet from above to replace the definition
4. Go to tests.api.test_parameters.test_formdata_file_upload
5. Use following code to replace the function

def test_formdata_file_upload(simple_app):
    app_client = simple_app.app.test_client()
    resp = app_client.post('/v1.0/test-formData-file-upload',
                           data={'formData': [(BytesIO(b'file contents'), 'filename1.txt'), (BytesIO(b'file contents'), 'filename2.txt')]})
    assert resp.status_code == 200
    response = json.loads(resp.data.decode('utf-8', 'replace'))
    assert response == {'filename1.txt': 'file contents'}

1. Observe test to pass, which it should not do.

Additional info:

Output of the commands:

• python --version -> 3.7.3
• pip show connexion | grep "^Version\:" -> master branch
• flask --version -> 1.1.0