Also keep the CSS file in alphabetical order so additions make
for clean diffs. (The async built file had a pseudo-random order)
Change-Id: Iad76ef36c90f42ba3232f135b05465408f42b2ba
Also produces a CSS file for the symbol buttons, using the
SVG filenames. Gets the list of symbols from symbols.json.
Bug: T118660
Change-Id: Iaa792418d870a7e266b6455ef037994e31278278