math.isnan and math.isinf should allow Decimal type

[brycepg]

The isinf and isnan can process decimal types:

import math
from decimal import Decimal
math.isnan(Decimal("nan"))

evaluates to True

Also isinf and isnan do no error out when passed int types. (Just always return false) Should that mean the stub should allow int to be passed as well?

[gvanrossum]

When float is declared, int is always accepted. For the math module in particular, it seems that it takes anything that can be converted to float. Maybe the signatures need to be changed to use typing.SupportsFloat?