tests: add support for install the tests

This will provide to run the tests using the gnome-desktop-testing [1] using the same environment that is used in meson.

There are some use cases that requires to run the unit-test on a post build step, in a different machine as the one that are used for build. The meson can run the test on a different target machine but this needs to be done at the build step.

The OpenEmbedded [2] always do cross compilation and run the tests in a post build step on a real or emulated machine, all the tests needs to be installed on the target. Using the OE-Core test infrastructure can be very useful for gstreamer project as OE-Core can run the unit-test on a vast range of different target architectures.

This MR add support for this use case, it's based and use the same logic as glib [3] with additional tweaks especially to install the environment used on meson to run the unit-test.

[1] https://wiki.gnome.org/Initiatives/GnomeGoals/InstalledTests

[2] https://www.openembedded.org/wiki/Main_Page

[3] https://gitlab.gnome.org/GNOME/glib/-/commit/1bba3276bb3b7a878860ac01483574599b23853c