This is a rewrite of add_glyphs in third_party/color_emoji. The
primary motivation was to move special aliasing rules out of that
code and use an external aliases file instead. This new version
is a bit more thorough about aliasing, and hopefully a little
easier to read.
The new add_glyphs takes its parameters using keywords, so
the invocation in the Makefile changed (as well as the path to
the tool).
emoji_aliases.txt was extended to add the flag aliases that were
formerly defined in the old add_glyphs code.
add_aliases was modified so the name of the alias file could be
passed in as a parameter to the main utility function that reads
the alias mapping from the file.
The new code expects all glyphs used by the template GSUB tables
to be named in the GlyphOrder table, but doesn't require the cmap
and hmtx table to be fleshed out. The new code fleshes these out
when it processes the sequences to add. As a result the cmap and
hmtx tables in the template were truncated.
The new code also sorts the GlyphOrder table when it extends/rebuilds
it.
Doug Felt