Change setinputsizes behavior for mssql+pyodbc

Change setinputsizes behavior for mssql+pyodbc

The ``use_setinputsizes`` parameter for the ``mssql+pyodbc`` dialect now
defaults to ``True``; this is so that non-unicode string comparisons are
bound by pyodbc to pyodbc.SQL_VARCHAR rather than pyodbc.SQL_WVARCHAR,
allowing indexes against VARCHAR columns to take effect. In order for the
``fast_executemany=True`` parameter to continue functioning, the
``use_setinputsizes`` mode now skips the ``cursor.setinputsizes()`` call
specifically when ``fast_executemany`` is True and the specific method in
use is ``cursor.executemany()``, which doesn't support setinputsizes. The
change also adds appropriate pyodbc DBAPI typing to values that are typed
as :class:`_types.Unicode` or :class:`_types.UnicodeText`, as well as
altered the base :class:`_types.JSON` datatype to consider JSON string
values as :class:`_types.Unicode` rather than :class:`_types.String`.

Fixes: #8177
Change-Id: I6c8886663254ae55cf904ad256c906e8f5e11f48