Add knob to never break line after named function parameter key

Similar to the issue described in https://github.com/google/yapf/issues/378, if the length of a named parameter key/value pair exceeds the `column_limit` yapf will split the line. This behavior is addressed for dictionary key/value pairs using the `ALLOW_SPLIT_BEFORE_DICT_VALUE` knob.

Is there an equivalent knob for named parameters in a function/constructor call? Perhaps the `ALLOW_SPLIT_BEFORE_DICT_VALUE` knob could be updated to affect such a case as well?

Example of current behavior:
```py
SchemaField(
'name',
'STRING',
mode='required',
description=
'Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc fringilla faucibus augue sed luctus. Nullam sapien leo, faucibus ac metus id, lobortis consectetur turpis. Phasellus imperdiet nisl pretium quam bibendum condimentum. Nulla sit amet mauris molestie, congue ipsum sed, mattis ex. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer dignissim faucibus ipsum, id iaculis dolor mattis sed. Mauris egestas aliquam dui, eget lobortis erat fermentum aliquet. Morbi iaculis augue rhoncus nisl sodales pharetra. Vivamus malesuada, lectus vel porta vestibulum, diam sem viverra nulla, eget consectetur nulla felis eget libero. Etiam sed velit vitae sem eleifend blandit. Donec viverra libero lorem, eu luctus tortor faucibus fermentum. Mauris vehicula ornare metus pharetra eleifend.',
),
```