Turn oracle BINARY_DOUBLE, BINARY_FLOAT, DOUBLE_PRECISION into floats

Turn oracle BINARY_DOUBLE, BINARY_FLOAT, DOUBLE_PRECISION into floats

The Oracle BINARY_FLOAT and BINARY_DOUBLE datatypes now participate within
cx_Oracle.setinputsizes(), passing along NATIVE_FLOAT, so as to support the
NaN value.  Additionally, :class:`.oracle.BINARY_FLOAT`,
:class:`.oracle.BINARY_DOUBLE` and :class:`.oracle.DOUBLE_PRECISION` now
subclass :class:`.Float`, since these are floating point datatypes, not
decimal.  These datatypes were already defaulting the
:paramref:`.Float.asdecimal` flag to False in line with what
:class:`.Float` already does.

Added reflection capabilities for the :class:`.oracle.BINARY_FLOAT`,
:class:`.oracle.BINARY_DOUBLE` datatypes.

Change-Id: Id99b912e83052654a17d07dc92b4dcb958cb7600
Fixes: #4264