Require modules with dependent (leaf) modules to run tests for those dependent modules before merging changes

If every change that went into qtdeclarative had to be tested with its dependent modules, then we could catch a lot more bugs and save a lot of time. Even if I still have to fix these issues, at least I will then know exactly which change caused it, rather than have to bisect, etc., and the person who wrote the patch can give me a heads up: "hey, a test in qtquickcontrols2 failed, how should we fix this?"