vterm: Really fix terminal resizing.
vterm: Really fix terminal resizing.

This involves putting the part to the scrollback buffer which is not
seen anymore after the shrink and also fixing cursor positioning if we
need to put back data from the scrollback buffer.

Additionally, scrolling regions are completely reset after a resize
event.

bk2204/urwid,wardi/urwid,rndusr/urwid,westurner/urwid,drestebon/urwid,tonycpsu/urwid,Julian/urwid,bk2204/urwid,wardi/urwid,Julian/urwid,drestebon/urwid,mountainstorm/urwid,hkoof/urwid,ivanov/urwid,douglas-larocca/urwid,westurner/urwid,drestebon/urwid,foreni-packages/urwid,rndusr/urwid,mountainstorm/urwid,hkoof/urwid,urwid/urwid,harlowja/urwid,inducer/urwid,zyga/urwid,inducer/urwid,rndusr/urwid,tonycpsu/urwid,douglas-larocca/urwid,ivanov/urwid,douglas-larocca/urwid,urwid/urwid,Julian/urwid,urwid/urwid,inducer/urwid,zyga/urwid,mountainstorm/urwid,ivanov/urwid,bk2204/urwid,foreni-packages/urwid,foreni-packages/urwid,harlowja/urwid,wardi/urwid,tonycpsu/urwid,zyga/urwid,westurner/urwid,hkoof/urwid,harlowja/urwid