Since KDEInstallDirs6 explicitly sets KDE_INSTALL_DIRS_NO_DEPRECATED to
false.

Fixes unit tests with Qt6 and identified the missing definition of the
full path variables for aliases.

Fixes a number of unit tests that rely on Qt in some form when using Qt6.

With this we are no longer skipping a bunch of tests when using Qt6.

This likely still misses forwarding the Qt option to the CMake calls of
the actual tests, but that's for a subsequent change.

There's a few modules relying on ECM_GLOBAL_FIND_VERSION being defined, so
set that. The exact value is less relevant here, it's mainly used for
deprecation warnings.

To avoid ambiguity with ECMQmlModule.cmake.

To preserve backward compatibility, we keep a version around of
ECMQMLModules.cmake that warns a user of it being moved and includes the
new file.

This contains some helper functions to make it easier to create QML
modules through CMake. It takes care of several things that currently
need to be done manually.

It adds four tests for the four primary ways that it can be used,
either as shared/static library and with or without C++ plugin.

While porting a manual configure_file invocation for kactivities'
.pc file to ecm_generate_pkgconfig_file I noticed that the URL keyword
was missing afterwards.