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/libneochat/CMakeLists.txt

@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: 2023 Tobias Fella <tobias.fella@kde.org>
+# SPDX-License-Identifier: BSD-3-Clause
+
+add_library(LibNeoChat STATIC)
+
+target_sources(LibNeoChat PRIVATE
+    delegatesizehelper.cpp
+)
+
+ecm_add_qml_module(LibNeoChat GENERATE_PLUGIN_SOURCE
+    URI org.kde.neochat.libneochat
+    OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/src/org/kde/neochat/libneochat
+)
+
+generate_export_header(LibNeoChat BASE_NAME LibNeoChat)
+target_link_libraries(LibNeoChat PUBLIC
+    Qt::Core
+    Qt::Quick
+)