FIX: Replace unnecessary eval() calls with literal_eval()

[jwiggins]

Drive-by while looking into RangeEditor strangeness.

[jwiggins]

I'm not 100% sure about this one because I don't have much experience with the editor.

[jwiggins]

I don't understand this failure. It doesn't seem related to the changes.

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FAIL: test_qt_process_events_process_all (traitsui.testing.tests.test_gui.TestProcessEventsRepeated)
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Traceback (most recent call last):
  File "D:\a\traitsui\traitsui\.edm\envs\traitsui-test-3.6-pyside2\lib\site-packages\traitsui\testing\tests\test_gui.py", line 152, in test_qt_process_events_process_all
    self.assertEqual(n_left_behind_events, 0, msg)
AssertionError: 8 != 0 : Expected 10 events processed on the objects and zero events left on the queue after running process_cascade_events. Found 2 processed with 8 left behind.

[corranwebster]

Failure looks to be unrelated, unless the change is causing tests to not clean up after themselves properly.

I'll open an issue.

Edit: #1977

[corranwebster]

Sat down and had a more thorough look at this and I think that literal_eval isn't the right thing for a bunch of these since many editors have an evaluate trait or method - eg. BaseRangeEditor provides this so at least the RangeEditor examples should probably replace eval with self.evaluate.

That feels like the right solution to propagate for most of these. However a sane default in some of these cases may be literal_eval and doing this in some cases may be an API change.