Custom objects returned by modules must be subclass of ModuleObject and
have the state argument in its methods.
Add MutableModuleObject base class for objects that needs to be deep
copied on assignation.
The only advantage they have is they have the interpreter in arguments,
but it's already available as self.interpreter. We should discourage
usage of the interpreter API and rely on ModuleState object instead in
the future.
This also lift the restriction that a module method cannot add build
targets, but that was not enforced for snippet methods anyway (and some
modules were doing it) and it's really loose restriction as it should
check for many other things if we wanted to make it consistent.
This is so dumb, we can just insert C for you without you having to know
that you're using C under the hood. This is nicer because:
1) Meson doesn't make the user add a language they're not explicitly
using
2) If there was ever an implementaiton of Vala that didn't use C as
it's assembly language, this wouldn't make any sense.
The build level shouldn't be deal with interpreter objects, by the time
they leave the intpreter they should be in the Meson middle layer
representaiton
We need to konw on rconfigure which options have already bee set not
just for the super project, but also for the subproject. However, using
first_invocation is not sufficient, as a reconfigure could add a new
subpproject that wasn't present before, and we need to initialize that
project's builtins.