[Process] Added a "isTtySupported" static method

[javiereguiluz]

It allows to enable the TTY mode everywhere it's available without risking an exception:

$process = (new Process)->setTty(Process::isTtySupported());

See #6188

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Sadly our docs about TTY, PTY, etc. are very lacking. There's an old issue about this --> #6188 We need to find someone who truly understand this well and explains it to us. Thanks!