gyp: muffle xcodebuild warnings

Muffle xcodebuild warnings by introducing an alternative quieter
alternative to GetStdout, called GetStdoutQuiet, and call it selectively
in particularly noisy xcodebuild commands.

Co-authored-by: Gibson Fahnestock <gibfahn@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/21999
Original-PR-URL: https://github.com/nodejs/node-gyp/pull/1370


Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>