You can now mark String message parameters with the [UTF8] attribute.
This will cause the generated decoder to perform UTF-8 validation and
reject the message if the given parameter is not a valid UTF-8 string.
This frees up the receiving side from having to do this validation at
a higher level.
This commit moves the clipboard from WindowServer into a new Clipboard
service program. Clipboard runs as the unprivileged "clipboard" user
and with a much tighter pledge than WindowServer.
To keep things working as before, all GUI::Application users now make
a connection to Clipboard after making the connection to WindowServer.
It could be interesting to connect to Clipboard on demand, but right
now that would necessitate expanding every GUI app's pledge to include
"unix" and also unveiling the clipboard portal, which I prefer not to.