The main QtcProcess interface is nowadays a CommandLine, with no
explicit references left to QtcProcess::Arguments and related static
helper functions, so it only clutters the QtcProcess class interface
So move these items out of QtcProcess, later potentially to a separate
file pair.
Change-Id: I45c300b656f5b30e2e2717232c855fdd97c2d1d7
Reviewed-by: Christian Stenger <christian.stenger@qt.io>