[88 new] Mono: heavy line-drawing characters

Managed to reproduce using FIG-let/TOI-let and the 'Future' font, with a sample-text such as:

  ╺┳╸┏━╸┏━┓╺┳╸ ╺┳╸┏━╸┏━┓╺┳╸ ╺┳╸┏━╸┏━┓╺┳╸
   ┃ ┣╸ ┗━┓ ┃ ┃ ┣╸ ┗━┓ ┃ ┃ ┣╸ ┗━┓ ┃
   ╹ ┗━╸┗━┛ ╹ ╹ ┗━╸┗━┛ ╹ ╹ ┗━╸┗━┛ ╹
  ┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸
  ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸ ┣╸
  ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹ ╹
  ╻ ╻┏┓ ╻ ╻┏┓╻╺┳╸╻ ╻ ┏┳┓┏━┓┏┓╻┏━┓
  ┃ ┃┣┻┓┃ ┃┃┗┫ ┃ ┃ ┃ ┃┃┃┃ ┃┃┗┫┃ ┃
  ┗━┛┗━┛┗━┛╹ ╹ ╹ ┗━┛ ╹ ╹┗━┛╹ ╹┗━┛
   

These are the Unicode "heavy" line drawing characters (equivalent of bold, except they stay the same for all weights). The line-drawing characters are not yet included and so are arriving via substitution from others monospace fonts of a different advance width (600), whereas the space character (' ') is coming Ubuntu Mono itself with a narrower advance width (500).

When rendered using a grid/cell renderer (such as the Terminal) then the substituted glyphs are 100 F-units oversize, but are still reset and kept to the grid before the next character position.

Where I've reproduced the issue, it shows up in other graphical applications such as the email client or web-browser (see attached screenshot). The number of spaces on some rows is significantly fewer than on other rows, thus causing the gradual degradation. In the following I've replaced the spaces with a mid-dot so it's hopefully easier to see what's happening:

  ╺┳╸┏━╸┏━┓╺┳╸···╺┳╸┏━╸┏━┓╺┳╸···╺┳╸┏━╸┏━┓╺┳╸
  ·┃·┣╸·┗━┓·┃·····┃·┣╸·┗━┓·┃·····┃·┣╸·┗━┓·┃·
  ·╹·┗━╸┗━┛·╹·····╹·┗━╸┗━┛·╹·····╹·┗━╸┗━┛·╹·
  ┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸┏━╸
  ┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·┣╸·
  ╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··╹··
  ╻·╻┏┓·╻·╻┏┓╻╺┳╸╻·╻···┏┳┓┏━┓┏┓╻┏━┓
  ┃·┃┣┻┓┃·┃┃┗┫·┃·┃·┃···┃┃┃┃·┃┃┗┫┃·┃
  ┗━┛┗━┛┗━┛╹·╹·╹·┗━┛···╹·╹┗━┛╹·╹┗━┛
  ·

These are from the Unicode Box Drawing range (U+2500…U+257F); there are 15 heavy box drawing characters: ━┃┏┓┗┛┣┫┳┻╋╸╹╺╻ but the full 128 contains all the various joining forms (heavy on one side, regular on the other).

We already have about a third of this block already done, so it probably makes just to do the rest (they only need doing once, and then straight copying to the other weights):

  http://unicode.org/charts/PDF/U2500.pdf