sixel: implement private mode 8452 (leave cursor right of graphics)
Private mode 8452 controls whether the cursor is left to the right of the emitted graphics (or on the next line).
Ps = 8 4 5 2 ⇒ Sixel scrolling leaves cursor to right of graphic.
Foot does not implement this, and always leaves the cursor on the next line.
XTerm default is not set (leave cursor on the next line).
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