chinese/fcitx: Fix options GTK2 and GTK3, improve port

GTK2 and GTK3 options aren't working properly: even if disable GTK2, it
gets re-enabled GTK2.

Improve port:

• Replace PORTVERSION with DISTVERSION.
• Fix warnings from portclippy.
• Set dependency from ecm as build.
• Convert CMAKE_ARGS to CMAKE_ON and CMAKE_OFF.
• Replace ".if ${PORT_OPTIONS:M***}" with new style options.
• Remove unnecessary KDE_MAN_PREFIX - it have default value.
• Remove description of Qt4 module from pkg-message.
• Use DESKTOPDIR in pkg-message.

PR: 294883
Approved by: lichray@gmail.com (maintainer)
Sponsored by: UNIS Labs
Co-authored-by: Ken DEGUCHI <kdeguchi@sz.tokoha-u.ac.jp>
MFH: 2026Q2