Hextris runtime packaged for PLAYCHIVE

Upstream repository: https://github.com/Hextris/hextris
Pinned revision: 3f4847dc8fd7dab3d1c87e6324b9159d92fbd396
Upstream project: https://hextris.github.io/hextris/

Hextris is GPL-3.0-or-later. This bundled directory retains the full upstream
license at HEXTRIS-GPL-3.0-OR-LATER.txt. The complete corresponding source is
available from the upstream repository above, and PLAYCHIVE's packaging script
is scripts/build-hextris-web.sh.

Packaging changes: Google font, Google Ads and Google Analytics references were
removed. All gameplay code, images, style sheets, sound generation and local
storage score handling are served from this directory; no playable data is
fetched from another site.