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/timelinedelegate.h

@@ -8,6 +8,8 @@
 
 #include <Kirigami/Platform/Units>
 
+#include "delegatesizehelper.h"
+
 /**
  * @brief The base Item for all delegates in the timeline.
  *
@@ -77,17 +79,8 @@ private:
     Kirigami::Platform::Units *m_units = nullptr;
     void setCurveValues();
 
-    qreal m_leftPadding;
-    qreal m_rightPadding;
+    DelegateSizeHelper m_sizeHelper;
 
-    qreal m_startBreakpoint;
-    qreal m_endBreakpoint;
-    int m_startPercentWidth = 100;
-    int m_endPercentWidth = 85;
-    qreal m_maxWidth;
-    int availablePercentageWidth() const;
-    qreal maxAvailableWidth() const;
-    qreal availableWidth() const;
     bool m_alwaysFillWidth = false;
 
     void resizeContent();