Subprocess does not freeze when it generates a lot of output to stdout

[Akirathan]

Fixes #9549

Pull Request Description

According to this SO answer, one has to first read the streams from java.lang.Process before calling process.waitFor(). Otherwise, the current thread will block. I have encountered this when I tried to invoke a subprocess via System.Process.run that generates a long output to its stdout.

Important Notes

Checklist

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• The documentation has been updated, if necessary.
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[Akirathan]

I tested it locally by invoking a subprocess that generates a lot of output. Any ideas for a unit test?