autotests: Use a shared library for the integration test framework

Ever since the effects were changed to static, each test of the
integration tests includes all the effects. The result of this is that
when doing a debug build each test is now 60MiB or more. With the amount
of tests, this results in ~8 GiB of diskspace used just for KWin's
binary output directory, which is rather excessive.

Since the tests all share a common framework library, we can change that
library to a shared library and that way avoid linking all the effects
into each test.

Most of this is shuffling around some link libraries in the integration
test CMakeLists, however, I needed to export the Xwayland class as it is
used by one of the tests but wasn't exported.