Doc: Fix qt_import_plugins snippet to use Qt6::

The documentation text uses Qt6:: instead of Qt::, so let's
also use that in the shown snippet. This is also the style
we promote for targets in other documentation pages.

While at it, print the target names consistently in monospace
font.

Pick-to: 6.7
Change-Id: Ia4d67bad2790d6688ef8d5b4103453c5c40877bc
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit e836f8794403696a8467b69f0ab822d36b01a18c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/doc/snippets/cmake-macros/examples.cmake

@@ -68,11 +68,11 @@ qt_generate_moc(main.cpp main.moc TARGET myapp)
 
 #! [qt_import_plugins]
 qt_add_executable(myapp main.cpp)
-target_link_libraries(myapp Qt::Gui Qt::Sql)
+target_link_libraries(myapp Qt6::Gui Qt6::Sql)
 qt_import_plugins(myapp
-    INCLUDE Qt::QCocoaIntegrationPlugin
-    EXCLUDE Qt::QMinimalIntegrationPlugin
-    INCLUDE_BY_TYPE imageformats Qt::QGifPlugin Qt::QJpegPlugin
+    INCLUDE Qt6::QCocoaIntegrationPlugin
+    EXCLUDE Qt6::QMinimalIntegrationPlugin
+    INCLUDE_BY_TYPE imageformats Qt6::QGifPlugin Qt6::QJpegPlugin
     EXCLUDE_BY_TYPE sqldrivers
 )
 #! [qt_import_plugins]

src/corelib/doc/src/cmake/qt_import_plugins.qdoc

@@ -89,7 +89,7 @@ In the snippet above, the following occurs with the executable \c myapp:
 \li The \c Qt6::QMinimalIntegrationPlugin plugin is
     excluded from being automatically imported into myapp.
 \li The default list of plugins for \c imageformats is
-    overridden to only include Qt6::QGifPlugin and Qt6::QJpegPlugin.
+    overridden to only include \c Qt6::QGifPlugin and \c Qt6::QJpegPlugin.
 \li All \c sqldrivers plugins are excluded from automatic importing.
 \endlist