[issue33610] IDLE: Make multiple improvements to CodeContext

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

While trying out variable lines, #33642, I encounter two related issues.

First is the context colors.  Black on gray is a variant of black on white.  I am using the dark theme, white on dark blue.  For fixed sized context, the high contrast is okay.  For variable context, having lines flip from light on dark to dark on light and back is distracting to obnoxious. So I want to change
9. Reenable user config of context colors?
to 
9. Reenable user config of context colors!
Add the current black on gray to the light theme and appropriate values, to be determined, to the dark theme.

Second is getting partial lines at the top of the text box as a result of scrolling with the mousewheel or scrollbar slider.  I never liked this but tolerated it.  With complete text lines above, it looks awful to me.  Hence, I consider the following to be a dependency of this issue.  
17. #33664 Scroll by lines instead of sometimes by pixels.

Following the implementation notes for #33664, once the label is changes to text, to get the target topline, 8. can be implemented with
text.xview_scroll(target_topline - current_topline, 'units')

I would like to release multiple user visible improvements at once, at least 7, 9, and 17, so the new code context looks good from the start.   8, menu changes, and 14 could come later.

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dependencies: +IDLE:  scroll text by lines, not pixels.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33610>
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