Alert clients to new symbolic scale value "float"

ODATA-557 proposes adding a new symbolic value "float" to the scale attribute for decimals to specify that values will be returned in exponential notation.

In OData V4 we should add text to make clients aware of this expected change;

"The Scale attribute value of "float" is reserved for future use for decimal types with precision of 16 or 34 to specify that values will be returned using exponential notation."