Utils: More forward declarations / drop unused headers [A-C]

Round 1 - focus on headers.
For classes with initial in range [A-C].
Try to keep the same separators between different kind of headers.

Change-Id: Ieab893d644af035c42590401c90728719394221f
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/python/pyside.h

@@ -29,6 +29,7 @@
 
 #include <utils/filepath.h>
 
+#include <QCoreApplication>
 #include <QTextDocument>
 
 namespace TextEditor { class TextDocument; }