Merge from vendor branch TNF:

Merge from vendor branch TNF:
Import xvkbd-3.2 as x11/xvkbd.
Packaged by Ryo ONODERA in pkgsrc-wip, PR#43851.

xvkbd is a virtual (graphical) keyboard program for X Window System
which provides facility to enter characters onto other clients
(softwares) by clicking on a keyboard displayed on the screen. This
may be used for systems without a hardware keyboard such as kiosk
terminals or handheld devices. This program also has facility to
send characters specified as the command line option to another
client.