Get GTK+ 4 installed-tests closer to working

While trying to update Debian's experimental gtk+4.0 package to GTK+ 3.94.0, I noticed that the installed-tests were not all installed correctly: the reftests tried to run executables from the wrong directory, the accessibility-dump helper wasn't installed, and the metadata file keywords.test tried to run a nonexistent executable named "keywords" (its name is really autotestkeywords).

The keywords.test error was the most serious, because gnome-desktop-testing-runner stops running tests when it encounters an error spawning a subprocess, and a missing executable (that is not wrapped in a shell one-liner) causes such an error.

With these patches applied, many installed-tests still fail, but at least they are all run.