If we want to use "qmake mixing" in Coin aka:

• Build qtbase with CMake
• Build qtwebengine with qmake

we need to somehow tell Coin to build qtbase with CMake, zip up the artifacts, and re-use them when building qtwebengine with qmake.

In order to accomplish that, we need to use the same configurations in qt5/coin/platform_configs/qtbase.yaml *and *qt5/coin/platform_configs/qtwebengine.yaml.

That means we can't use the UseLegacyInstructions feature in qtwebengine.yaml, because qtbase which is built with CMake doesn't have that feature, and thus the qtbase artifacts won't be used.

That also means that we need to convert the old legacy instruction qmake configurations to use .yaml files for build and test instructions.

Thus we can have both qtbase and qtwebnegine use yaml instruction files, with the difference that the qtbase .yaml instructions will use CMake, whereas the qtwebengine configs will use qmake in side their .yaml instruction files.

Note that qtbase will have to have 2 sets of instructions files, ones using qmake and ones using CMake. That will be the case until we completely switch over to using CMake, and the qmake instructions can be removed. Thus we have to delegate the choice of which build system to use for a specific config, probably via an environment variable or some feature value (do we support random strings like "qmake" or "cmake" in the Features key?)