Improve 'from import' detection in BadModuleAttributeUseLinter

[mschwager]

There is currently room for false positives and false negatives in BadModuleAttributeUseLinter. Consider the following:

from foo import bar

bar.baz("example")

import foo

foo.bar.baz("example")

Currently, to catch both of these use cases we have to use two illegal module attributes:

@property
def illegal_module_attributes(self):
    return {
        'foo.bar': [
            'baz',
        ],
        'bar': [
            'baz',
        ],
    }

This is bad for two reasons:

1. Developers implementing new BadModuleAttributeUseLinter classes may not realize they have to include both (or more), which opens the door for false negatives. I.e. illegal attributes are being used, but not detected.
2. False positives can arise in the bar.baz case. E.g.

from foo import bar  # bad
from qux import bar  # okay

bar.baz("example")

We should improve detection in BadModuleAttributeUseLinter to account for this. We should also make it work for arbitrary depth imports, e.g. one illegal module attribute definition should catch all of these:

import really
from really import long
from really.long import deep
from really.long.deep import import_statement

really.long.deep.import_statement("example")

@property
def illegal_module_attributes(self):
    return {
        'really.long.deep': [
            'import_statement',
        ],
    }

Instead of requiring multiple:

@property
def illegal_module_attributes(self):
    return {
        'really.long.deep': [
            'import_statement',
        ],
        'long.deep': [
            'import_statement',
        ],
        'deep': [
            'import_statement',
        ],
    }