Finish rearranging the methods of configdialog.ConfigDialog to group together methods pertaining to each tab and the button block.  Doing so has and will help in writing tests.  It is also preparation for splitting ConfigDialog, which currently has more than 70 methods, into multiple more maintainable classes.

#30993, pr2831 moved the methods pertaining to the font tab right after create_font_tab.  #31003, pr2859 did the same for methods pertaining to the general tab.  In both case, the generated diff had a + block at the new location and - block at the old locations.

When I did the same for the highlight tab for #31001, the number of methods and lines moved was perhaps doubled, which meant that more of the other lines changed position.  The result was a huge diff, by default unrendered, that deleted and inserted most of the lines in the file.  Adding real edits on top of this would result in a worse huge diff.

So I decided instead to open this issue and finish method movement (for the dialog, button group, and keys group) to the extent I can now.  (The order within groups may be adjusted later as tests are written and knowledge about the methods is gained.)