Support an allowlist of function calls in argument defaults for B008

It would be great if B008 supported an allowlist of function calls, similar to `extend-immutable-calls` for B006. We do a lot of this in our code which as far as I know has no subtle bugs:

```python
def f(x=Decimal("1000")):
    pass
```

Or maybe it's worth hardcoding `Decimal` as an exception?