autoCloseBrackets misbehaves with Python string prefixes

Entering ' in a Python editor will automatically insert the closing ', as it does for brackets. Entering u', r', ur' or b' (case-insensitive) may also indicate the start of a string, but is misinterpreted as closing a string, so ' is not auto-inserted. Entering an empty byte-string (in Python 3), b'' will automatically append a third apostrophe!

Similarly, the heredoc-like string syntax in Python is not supported: ''' should be closed by ''' (instead, a fourth apostrophe is inserted); """ should be closed by """.

[haraldschilly]

another case a python 3.6 “format strings”, i.e. they start with f" or f' or for raw strings, e.g. rf'a b \n {x} d' is a prefix of rf is possible.

[jasongrout]

For completeness, checking for word characters prevents don't from turning into don''t, for example.