QDoc manual: Correct CMake command manual examples

The manual places CMake metadata commands on namespaces, although QDoc
accepts them only for modules. Its copied HTML output also obscures what
each command actually generates.

Show valid module-level examples and the resulting CMake commands
directly, including the Qt-specific target override.

Pick-to: 6.12
Change-Id: I7072087d2c0ca8757b77eec8929abb84cdec77e0
Reviewed-by: Topi Reinio <topi.reinio@qt.io>