It took a while to clean up the source vectors (converting strokes to outlines, joining paths w/ union, subtract, intersect, difference properly, flattening things, getting alignment correct, getting things exported properly, etc).
Once that was all figured out, imported the cleaned up icons into IcoMoon and prepared for export. Retrieved the relevant TTF fonts and JSON config from IcoMoon and replaced the existing fonts/config in the project.
Everything continues to look as expected (or better), but a few icon names have changed. I'll add the icon name changes to this diff to avoid spamming Phabricator with a bunch of rename diffs.
We're now including the entire SWMansion icon pack (all 275 icons) so we should hopefully never have to look at this again. If we have additional icons we want to include in the future, they'll live in (the much smaller) CommIcons pack.