Add list of 3rd party code attributions to Qt Core, Qt GUI, Qt SQL

Also document the current license the modules are available from,
since this is not consistent anymore across Qt.

Task-number: QTBUG-55139
Change-Id: I117fdb0cda7bd7ff92aa825e29c28f22a8a2f96d
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

src/corelib/doc/src/qtcore-index.qdoc

@@ -101,7 +101,19 @@
     \li \l{The Event System}
     \endlist
 
-    \section1 Related Information
+    \section1 Licenses and Attributions
+
+    Qt Core is available under commercial licenses from \l{The Qt Company}.
+    In addition, it is available under the
+    \l{GNU Lesser General Public License, version 3}, or
+    the \l{GNU General Public License, version 2}.
+    See \l{Qt Licensing} for further details.
+
+    Furthermore Qt Core potentially contains third party
+    modules under following permissive licenses:
+
+    \generatelist{groupsbymodule attributions-qtcore}
+
     \section1 Reference
     These are links to the API reference materials.
     \list

src/gui/doc/src/qtgui.qdoc

@@ -187,6 +187,19 @@
 
     More info in \l{Drag and Drop}
 
+    \section1 Licenses and Attributions
+
+    Qt GUI is available under commercial licenses from \l{The Qt Company}.
+    In addition, it is available under the
+    \l{GNU Lesser General Public License, version 3}, or
+    the \l{GNU General Public License, version 2}.
+    See \l{Qt Licensing} for further details.
+
+    Furthermore Qt GUI potentially contains third party
+    modules under following permissive licenses:
+
+    \generatelist{groupsbymodule attributions-qtgui}
+
     \section1 Reference
     \list
     \li \l{Qt GUI C++ Classes}

src/sql/doc/src/qtsql.qdoc

@@ -51,6 +51,19 @@
     QT += sql
     \endcode
 
+    \section1 Licenses and Attributions
+
+    Qt SQL is available under commercial licenses from \l{The Qt Company}.
+    In addition, it is available under the
+    \l{GNU Lesser General Public License, version 3}, or
+    the \l{GNU General Public License, version 2}.
+    See \l{Qt Licensing} for further details.
+
+    Furthermore Qt SQL potentially contains third party
+    modules under following permissive licenses:
+
+    \generatelist{groupsbymodule attributions-qtsql}
+
     \section1 Related Information
 
     These are links to the API reference materials and related pages.