New job: KTerminalLauncherJob
This replaces KToolInvocation::invokeTerminal, and builds on top of (actually, inherits) KCommandLauncherJob.
And this time it comes with unittest and command-line test program.
The Windows code path is especially interesting. It's all ported from ktoolinvocation_win.cpp. The part in kterminallauncherjob.cpp was fully tested on Linux (by swapping the ifdefs everywhere). The Windows-specific flags and handling of arguments in KProcessRunner needs testing on Windows though.
KF6 task: https://phabricator.kde.org/T14329