The current conformance test suite is suboptimal in many ways.

All tests are built into the same binary, which makes adding new tests,
builting tests, and running groups of tests much more awkward than it
needs to be. The first issue, especially, raises the bar of contribution
in a significant way, while the other two take their toll on the
maintainer. All of these changes were introduced back when we had both
Clutter and Cogl tests in tree, and because we were building the test
suite for every single change; since then, Cogl moved out of tree with
all its tests, and we build the conformance test suite only when running
the `check` make target.

This admittedly large-ish commit changes the way the conformance test
suite works, taking advantage of the changes in the GTest API and test
harness.

First of all, all tests are now built separately, using their own test
suite as defined by each separate file. All tests run under the TAP
harness provided by GTest and Autom...