x11-toolkits/gtk30: fix pkg-plist with BROADWAY option disabled

After the update to 3.24.38, with the BROADWAY option disabled, the port
fails to package, with:

pkg-static: Unable to access file /wrkdirs/share/dim/ports/x11-toolkits/gtk30/work/stage/usr/local/man/man1/broadwayd.1.gz:No such file or directory

Add %%BROADWAY%% prefixes to more broadway-related files in pkg-plist
(broadwayd.1.gz, broadwayd.html and gtk-broadway.html).

PR: 275567
Fixes: 0a1dd69c3167