Certain glyphs are counted double in QTextEdit ("non-BMP code points that are represented using surrogate pairs")

Opening or pasting text in(to) a QTextEdit view that has UTF16 glyphs leads to the following observations:

• the glyphs are shown correctly if a suitable (fallback) font is available
• the cursor behaves as expected when controlled via the keyboard: 1 press only is required to move the cursor over the glyphs in question, or to delete them.
• the reported column position is wrong, and counts each of these glyphs twice.

A small demonstrator program: github.com/RJVB/qtwheeltest ; build and start with the `–QTextEdit` option, then copy the text from the attachment into the top window (the one that has protected and the col/line numbers in the titlebar).