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.

testing/python/collect.py

@@ -1003,9 +1003,9 @@ class TestTracebackCutting:
         with pytest.raises(pytest.skip.Exception) as excinfo:
             pytest.skip("xxx")
         assert excinfo.traceback[-1].frame.code.name == "skip"
-        assert excinfo.traceback[-1].ishidden()
+        assert excinfo.traceback[-1].ishidden(excinfo)
         assert excinfo.traceback[-2].frame.code.name == "test_skip_simple"
-        assert not excinfo.traceback[-2].ishidden()
+        assert not excinfo.traceback[-2].ishidden(excinfo)
 
     def test_traceback_argsetup(self, pytester: Pytester) -> None:
         pytester.makeconftest(