Knit tests: check if the produced code is valid TypeScript

[aSemy]

Currently the Knit tests only do a string comparison. But that doesn't mean the expected string is correct TypeScript...

1. add the Gradle Node plugin, download TypeScript
2. download TypeScript npx task
3. in the tests, try compiling the generated TypeScript using a command line arg npx tsc (somehow? I'm not sure about this...)
4. Check there's no errors (again, I'm not sure)