DataRange2D set_bounds method fires multiple events

**Problem Description**
The goal of ``set_bounds`` is to update all the bounds simultaneously under one event. Current implementation fires multiple events (depending on how many values have changed).

**Reproduction Steps:**
Checked by writing a unittest for ``DataRange2D``

```python
def test_set_bounds_events(self):
with self.subTest(msg="DataRange2D"):
r = DataRange2D()
with self.assertTraitChanges(r, 'updated', count=1):
r.set_bounds((-1, -2), (3, 4))

with self.subTest(msg="DataRange2D.x_range"):
r = DataRange2D()
with self.assertTraitChanges(r.x_range, 'updated', count=1):
r.set_bounds((-1, -2), (3, 4))

with self.subTest(msg="DataRange2D.y_range"):
r = DataRange2D()
with self.assertTraitChanges(r.y_range, 'updated', count=1):
r.set_bounds((-1, -2), (3, 4))
```
Output from each subtest:
```
FAIL: test_set_bounds_events (chaco.tests.test_datarange_2d.DataRange2DTestCase) [DataRange2D]
...
AssertionError: Change event for updated was fired 4 times instead of 1

FAIL: test_set_bounds_events (chaco.tests.test_datarange_2d.DataRange2DTestCase) [DataRange2D.x_range]
...
AssertionError: Change event for updated was fired 2 times instead of 1

FAIL: test_set_bounds_events (chaco.tests.test_datarange_2d.DataRange2DTestCase) [DataRange2D.y_range]
...
AssertionError: Change event for updated was fired 2 times instead of 1
```

**Expected behavior:**

The call to this method should fire only one event on DataRange2D and associated DataRange1D instances.