\## Description
Fixes#6921.
Added tests that fail before and pass afterwards.
Remove the check for `connection.in_atomic_block` to determine if the current request is under a `transaction.atomic` from `ATOMIC_REQUESTS`. Instead, duplicate the method that Django itself uses [in BaseHandler](964dd4f4f2/django/core/handlers/base.py (L64)).
This requires fetching the actual view function from `as_view()`, as seen by the URL resolver / BaseHandler. Since this requires `request`, I've also changed the accesses in `get_exception_handler_context` to be direct attribute accesses rather than `getattr()`. It seems the `getattr` defaults not accessible since `self.request`, `self.args`, and `self.kwargs` are always set in `dispatch()` before `handle_exception()` can ever be called. This is useful since `request` is always needed for the new `set_rollback` logic.
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