redesign box drawing to fit 137 code points in less space

redesign box drawing to fit 137 code points in less space

The 5 7x7 box figures can be condensed into 3 with similar aesthetics,
more concisely targeted to:
- simple single and double lines (IBM CP850 superset),
- single/double transitions and round corners (previously 3rd and 4th boxes,
  includes all IBM CP437 lines),
- heavy lines and diagonals (5th box with 1st innards).

Introduce another such drawing featuring all dashed lines (including
previously missing quadruple dashed horizontal lines) and block quadrants
(still missing ▚ and ▞).

Keep some smaller figures for heavy line combinations, introducing a single
#-shape to cover half line endings as well as 4 additional heavy transitions,
though various other such code points are still missing.