New text-line-wrap visual tests

Requested by @springmeyer @ https://github.com/mapnik/mapnik/issues/2427
Looks like when `wrap-character` used then `wrap-width` is ignored. Is this intended? This is not right behaviour I think.

Also I noticed that `dy` setting works different for Latin and Cyrillic scripts. For Cyrillic script it looks like `dy`*2. Wondering why…


P. S.: This is my first pull ever, so sorry about things like `text-line-wrap-512-512-1.0-grid-reference.json → text-line-wrap-800-450-1.0-grid-reference.json`. I don't know how to fix this.