Import most of the forkphorus test suite

Author: GarboMuffin

test/fixtures/execute/README.md

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 Tests in this folder are run in scratch by integration/execute.js. The tests can SAY test messages that map to tap methods. Read integration/execute.js for more.
 
 Tests whose names start with `tw-` are added by TurboWarp. Some of these tests are based on real projects from the scratch.mit.edu website, in which case their filename contains the original project ID and additional credits are within the project's scripts. We believe our use of these projects is fair use as the projects have been sufficiently modified and stripped down such that the project found here bears not even a slight resemblance to the original project.
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+Tests whose names start with `forkphorus-` were imported from https://github.com/forkphorus/forkphorus/tree/master/tests. There is a fair bit of test case sharing between forkphorus and TurboWarp.