delegatesizehelper updates

Make `DelegateSizeHelper` take a `QQuickItem` rather than a width value and move `TimelineDelegate` to use it rather than duplicting the code.

This requires the creation of `LibNeoChat` so that both the main and timeline modules can get access to the class.

Note: ideally more stuff will go into `LibNeoChat` but it turns out our dependencies are kinda spaghetti like and so will take some untangling.

src/timeline/CMakeLists.txt

@@ -90,4 +90,5 @@ ecm_add_qml_module(timeline GENERATE_PLUGIN_SOURCE
 target_link_libraries(timeline PRIVATE
     Qt::Quick
     KF6::Kirigami
+    LibNeoChat
 )