Bug with math.ceil returning float

[Algebra8]

The current implementation of Starlark's math.ceil will always return a starlark.Float as a result of being wrapped by newUnaryBuiltin.

Python's math.ceil, however, will always return an integral, as can be seen in the docs.

Also, Python's math.ceil will return an error when called with non-finite numeric values, i.e. nan, +inf, and -inf:

>>> math.ceil(float("nan"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: cannot convert float NaN to integer
>>> math.ceil(float("inf"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: cannot convert float infinity to integer
>>> math.ceil(float("-inf"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: cannot convert float infinity to integer

But Starlark's implementation allows for them, as can be seen in the tests:

...
assert.eq(math.ceil(inf), inf)
assert.eq(math.ceil(nan), nan)
...
assert.eq(math.ceil(-inf), -inf)
...

This bug was first mentioned in #370, as can be seen in this thread.

Possible solution:

Extract math.ceil from newUnaryBuiltin into its own function, ceil, that returns the result as an integral and returns an error when said result is not finite.