code: stop storing weakref to ExceptionInfo on Traceback and TracebackEntry

TracebackEntry needs the excinfo for the `__tracebackhide__ = callback`
functionality, where `callback` accepts the excinfo.

Currently it achieves this by storing a weakref to the excinfo which
created it. I think this is not great, mixing layers and bloating the
objects.

Instead, have `ishidden` (and transitively, `Traceback.filter()`) take
the excinfo as a parameter.

src/_pytest/python.py

@@ -1814,7 +1814,7 @@ class Function(PyobjMixin, nodes.Item):
                     if not ntraceback:
                         ntraceback = traceback
 
-            excinfo.traceback = ntraceback.filter()
+            excinfo.traceback = ntraceback.filter(excinfo)
             # issue364: mark all but first and last frames to
             # only show a single-line message for each frame.
             if self.config.getoption("tbstyle", "auto") == "auto":