Port the xterm, webgl, search, serialize and image source patches to upstream
08829c7. Where upstream fixed the same bug (#6204 mouse NaN guard, #6226 warm-up
cancel on dispose, #6235/#6237 serialize width clamp) take upstream and keep only
Orca's remaining delta (domContainer warm-up gate, clipped wide-cell blanking).
Bump mobile's webgl subset patch alongside. Drop serialize fuzz seed normal:5,
which now round-trips.
