Add test_turtledemo for colorizer in turtledemo

[terryjreedy]

A colorizer change could potentially break the use of colorizer in turtledemo.main. Relevant code:

 92 from idlelib.colorizer import ColorDelegator, color_config
 93 from idlelib.percolator import Percolator
# __init__ creates root and on line 166 calls makeTextFrame
# makeTextFrame(self, root) (line 211) makes a Frame and then a Text
213         self.text = text = Text(text_frame, ...
215         color_config(text)  
# After call to makeTextFrame() in def __init__().
195         Percolator(self.text).insertfilter(ColorDelegator())

The Percolator call can and should follow the color_config call. I propose to move the imports and those two lines to a new setup_colorizer(text) function in colorizer.py. Next add from idlelib.colorizer import setup_colorizer and setup_colorizer(text) to turtledemo. Then add a simple test of setup_colorizer to test_colorizer: create root, add Text, setup_colorizer, add some text with special items, and check that they are tagged. Branch is colordemo.

[terryjreedy]

An extracted function with docstring should be added to SO answer. See 2024 comment by TheLizard and reference to comment about 'hit' in colorizer.
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