Mozilla Public License 2.0

The GPL family of licenses are not perfect. Notably they are incompatible with
the SIL OFL 1.1 used by the fonts in scratch-render-fonts. In the packager we
'statically link' all of this those fonts into one HTML file. Is that legal?
Seems like you can make an argument that it's not. Who knows. I'm not a lawyer.

MPL 2.0 is a good alternative: It's still copyleft, used by real projects,
backed by a real organization, and GPL compatible.

Before c78e1c0 all changes were either by me
or under BSD3c. There are no third-party LGPL commits. Thus we can make this
switch.

Related: TurboWarp/scratch-gui#909