qdoc: Consolidate and emphasize \deprecated messages for QML and C++

Compare the links at https://doc.qt.io/qt-6/obsoleteqmltypes.html with those at https://doc.qt.io/qt-6/obsoleteclasses.html

Suggestions

• Add bolded notices at the top of the pages of deprecated QML types, similar to what C++ classes have: "This type is deprecated since 6.5. We strongly advise against using it in new code."
• Move the "deprecation reason"/"suggested alternative" text from the "Detail Description" section to the end of the bolded notice.

Examples

• https://doc.qt.io/qt-6/qwebenginequotarequest.html should say at the top, "This class is deprecated since 6.5. We strongly advise against using it in new code. Requesting host quota is no longer supported by Chromium."
• https://doc.qt.io/qt-6/qml-qtwebengine-quotarequest.html should say at the top, "This type is deprecated since 6.5. We strongly advise against using it in new code. Requesting host quota is no longer supported by Chromium."
• https://doc.qt.io/qt-6/qml-qt-labs-settings-settings.html should say at the top, "This type is deprecated since 6.5. We strongly advise against using it in new code. Use Settings from Qt QML Core instead."

Rationale

Normally, the first line of the Detailed Description is a short summary of the class/type. Displacing that summary with a "deprecation reason"/"suggested alternative" can cause surprise. Instead, writing that "deprecation reason"/"suggested alternative" as a continuation of the deprecation notice makes it much clearer.