fontique query matching algorithm

[dhardy]

A fontique::Query currently:

1. Filters available fonts by those matching any family in the given list
2. Extends the list of selected fonts using those matching the fallback script and locale, if provided
3. Finds the "best" match (according to given attributes) in each of the above-selected families and the default member of the family (if not equal to the best)

Problems:

• Support resolving multiple font files in the same file covering different unicode ranges #322: members of a family do not necessarily all cover the same unicode range.
• Locale and script have no impact on font preference, only on available fallbacks.
• Similarly, the font's "functional unicode range" has no impact on font preference (see here, considering arrows which do not use a specific script or locale).
• Query caching is internal, supporting only the last query. In contrast, kas-text caches all queries.

[dhardy]

I'm not sure exactly how matching should work, but from what I understand fontconfig uses a "distance" metric to sort all possible matches. CC @valadaptive

Another possible angle is to return multiple lists, e.g. "preferred fonts" then "all fonts with suitable attributes". This is likely insufficient since e.g. if one requests compressed-width fonts but has Arabic text, there likely won't be a matching font.