Why is TabularEditor slow?

Creating a tabular editor which displays 5 items takes 0.3 seconds, of which 70% is spent in the `_TableView.setModel` method.

https://github.com/enthought/traitsui/blob/8c21ab1fe9f526cf4ffcc1901739ca4661a7a450/traitsui/qt4/tabular_editor.py#L719

script to profile tabular editor

```
import cProfile
import os

from importlib_resources import files

from traits.api import HasTraits, Instance, List, Property
from traitsui.api import ModelView, TabularAdapter, TabularEditor, UItem, View

IMAGES_DIR = files('traitsui') / 'images'

class DataContainer(HasTraits):

_data = List()

def add_data(self, data_item):
self._data.append(data_item)

class DataContainerTabularAdapter(TabularAdapter):
columns = [('name', 'name')]

name_image = Property()

def _get_name_image(self):
return os.fspath(IMAGES_DIR / 'frame.png')

name_text = Property()

def _get_name_text(self):
return "test text"

model_view = Instance(ModelView)

class DataContainerModelView(ModelView):

model = Instance(DataContainer)

def default_traits_view(self):
body = UItem(
'model._data',
editor=TabularEditor(
adapter=DataContainerTabularAdapter(model_view=self),
editable=True,
operations=['move'],
show_titles=False,
vertical_lines=False,
horizontal_lines=False,
multi_select=True,
),
springy=True,
)

return View(body, resizable=True)

def main():
profile = cProfile.Profile()
profile.enable()

class Foo(HasTraits):
pass

model = DataContainer()
for _ in range(5):
model.add_data(Foo())

model_view = DataContainerModelView(model=model)
model_view.edit_traits()
profile.disable()
profile.dump_stats(
"C:\\Users\\rporuri\\work\\github\\ets\\traitsui\\temp\\test.prof"
)

if __name__ == '__main__':
main()
```

Ths zip file - [test.zip](https://github.com/enthought/traitsui/files/6310472/test.zip) - contains a single file - the profile data.

```
>>> from pstats import Stats
>>> s = Stats("C:\\Users\\rporuri\\work\\github\\ets\\traitsui\\temp\\test.prof")
>>> s.strip_dirs().sort_stats('cumtime').print_stats(0.025)
Wed Apr 14 16:50:07 2021 C:\Users\rporuri\work\github\ets\traitsui\temp\test.prof

35863 function calls (34827 primitive calls) in 0.312 seconds

Ordered by: cumulative time
List reduced from 739 to 18 due to restriction <0.025>

ncalls tottime percall cumtime percall filename:lineno(function)
1 0.000 0.000 0.312 0.312 handler.py:417(edit_traits)
1 0.000 0.000 0.309 0.309 view.py:374(ui)
1 0.000 0.000 0.308 0.308 ui.py:228(ui)
1 0.000 0.000 0.308 0.308 toolkit.py:167(ui_live)
1 0.000 0.000 0.297 0.297 ui_live.py:50(ui_live)
1 0.000 0.000 0.297 0.297 ui_live.py:69(_ui_dialog)
1 0.000 0.000 0.297 0.297 ui_base.py:294(display_ui)
1 0.000 0.000 0.248 0.248 ui_live.py:82(init)
1 0.000 0.000 0.240 0.240 ui_panel.py:258(panel)
1 0.000 0.000 0.231 0.231 ui_panel.py:497(__init__)
1 0.000 0.000 0.231 0.231 ui_panel.py:723(_add_items)
1 0.000 0.000 0.225 0.225 editor.py:234(prepare)
1 0.000 0.000 0.225 0.225 tabular_editor.py:144(init)
1 0.000 0.000 0.224 0.224 tabular_editor.py:138()
1 0.005 0.005 0.224 0.224 tabular_editor.py:711(__init__)
1 0.218 0.218 0.218 0.218 {built-in method setModel}
1 0.047 0.047 0.048 0.048 {built-in method show}
13/2 0.000 0.000 0.016 0.008 :966(_find_and_load)
```