This adds some additional flags to the default set. In addition,
it contains code that creates ligatures for some flag sequences to
others, for a few cases where we want different regions to share
the same flag. Finally, it adds default ligatures so that pairs of
regional indicator characters for which there's no predefined glyph
get a 'missing flag' glyph. This avoids cases where sequences of
regional indicator sequences accidentally match at odd locations
because of a previous mismatch.
There is no actual 'missing flag' glyph yet. The code uses an
existing emoji as a placeholder.
Doug Felt