task-malayalam*: Migrate from fcitx4 to fcitx5

For task-malayalam, the input method support was last changed from scim to fcitx (4.x) 12 years ago at [1]. Now considering that the fcitx 4.x upstream support is officially dead [2], we should move to the supported fcitx5 instead.

This commit contains the following changes:

• fcitx -> fcitx5
• fcitx-table-malayalam-phonetic -> fcitx5-table-malayalam-phonetic
• fcitx4 gtk2/gtk3 frontend -> fcitx5 gtk2/gtk3/gtk4 frontend
• fcitx4 qt5 frontend -> fcitx5 qt5/qt6 frontend
• fcitx4 KDE config -> fcitx5 KDE config

Besides, the dependency to fcitx4 GTK config GUI tool is removed since the fcitx5 upstream is only providing a Qt/KDE frontend GUI config tool at this moment.

This commit would resolve https://bugs.debian.org/1087657 .

[1] efee9baf [2] https://lists.debian.org/debian-input-method/2024/10/msg00042.html