[Egyptian Text] "Overlay middle" must be improved

The control character for "overlay middle" must be improved. The overlay looks good if both signs have a quadrant width. But if one sign is narrower and doesn't need the full quadrant width, the result is unbalanced and can even partly overlay the following sign (group) when it doesn't fill its own quadrant either. See here:

The owl takes the full quadrant width, so that the combination with the arm looks good. But neither the quail chick nor the ḥw.t-sign takes the full quadrant width, so that the overlaying arm is shifted to the right and can overlay a consecutive sign (see also the Cursor position at the end).

Start by reproducing the Egyptian Text “overlay middle” examples shown in the issue, comparing the owl case with the quail chick and ḥw.t-sign cases. Trace the control-character handling and check the cursor position at the end; done means narrow signs remain balanced without overlapping the following sign.

Written by the indexing model from the issue text.