Convert properties to decorator syntax

[JoeSchiff]

Description

spaCy uses a legacy syntax for defining properties in a Cython extension class which has been deprecated since ~2016:
https://cython.readthedocs.io/en/stable/src/userguide/extension_types.html#properties

Switching to the new syntax required moving the property docstrings. Previously, the docstring was placed on the line below the property keyword. However, using the new syntax there can not be anything between the decorator and the def statement, so the docstring was moved to below the def statement.

Types of change

Syntax change only

Checklist

• [X ] I confirm that I have the right to submit this contribution under the project's MIT license.
• [X ] I ran the tests, and all new and existing tests passed.
• [X ] My changes don't require a change to the documentation, or if they do, I've added all required information.