Ext and External were used inconsistently in the code and the
docs. This change converts all uses of Ext to External, including
within variable names used by the generator.
CPACK_EXT_ENABLE_STAGING enables optional staging
and CPACK_EXT_PACKAGE_SCRIPT allows to specify an optional
script file that can package staged files via an
external packaging tool.
Issue: #18236
The documentation for CPack generators previously lived in their
respective internal CMake modules. This setup was misleading,
because it implied that you should include the modules in your own
code, which is not the case. Moving the documentation into a
separate section does a better job of hiding the internal modules,
which are just an implementation detail. The generator documentation
has also been modified to remove any references to the module name.
The CPackIFW module is a special exception: since it has user-facing
macros, the documentation for these macros has been kept in the module
page, while all other documentation related to the IFW generator has
been moved into the new section.
To make it easier to find the new documentation, the old help pages
for the CPack*.cmake modules have not been deleted, but have been
replaced with a link to their respective help page in the new
documentation section.
