Log Message:
xorgproto: update to 2021.3.

If you thought the 2021.2 release was exciting, well, you're in
for a surprise: this one even builds with meson! How cool is that?!

Somewhat related: the new script to generate and verify the keysyms
was missing from the (autotools-generated) tarball, causing a meson
build from that tarball to fail during the setup phase. This is
fixed now.

No changes to the rest of the sources, so this is effectively
identical to yesterday's tarball.