chore: add spoon-test to check that spoon works on any repo

[monperrus]

I propose to add a script spoon-test as follows:

spoon-test https://github.com/google/guava

It would:

• check that the model can be built without any exception (contract inspired from build.sh)
• check that the pretty-printed code can be compiled with any exception (contract inspired from build.sh)
• check that the pretty-printed code passes all the test (contract inspired from build.sh)
• check all contracts on the model (see review: Generic contracts are run only on **.testclasses.** #2716)

This is basically a rework or extension of build.sh. We may consider a clean Python or Groovy version instead of this Shell monster.

[surli]

We may consider a clean Python or Groovy version instead of this Shell monster.

+1