Add `kdeclarative` as runtime dependency

I'm adding kdeclarative as a runtime dependency in order for Tokodon to run.

Before installing kdeclarative, I wasn't able to open Tokodon. I received the following in stdout:

user@host $ tokodon 
QQmlApplicationEngine failed to load component
qrc:/qt/qml/org/kde/tokodon/content/ui/Main.qml:357:30: Type SearchField unavailable
qrc:/qt/qml/org/kde/tokodon/content/ui/SearchField.qml:31:23: Type SearchView unavailable
qrc:/qt/qml/org/kde/tokodon/content/ui/SearchView.qml:124:13: Type PostDelegate unavailable
qrc:/qt/qml/org/kde/tokodon/content/ui/PostDelegate/PostDelegate.qml:263:30: Type PostMenu unavailable
qrc:/qt/qml/org/kde/tokodon/content/ui/PostDelegate/PostMenu.qml:9:1: module "org.kde.kquickcontrolsaddons" is not installed

After consulting the Plasma guide and finding kquickcontrolsaddons as part of the kdeclarative, I figured out that kdeclarative (for the latest KDE Plasma 6) needed to be installed as a runtime dependency.