Support spawn gating

[jiska2342]

Frida has a feature called spawn gating, where it attaches to launchd and awaits a process by its identifier (com.apple.foobar or similar). This is particularly useful when the target is not an app, but a process that is initialized through launchd, and in general to capture early startup of a process.

It would be great to add this as a command line option to gxpc :)

In the Frida command line tools, it is using the flag -W. Here is the Python source code for this, not sure about the Go bindings:
https://github.com/frida/frida-tools/blob/0c7caeae0e4b08d1ec36a922515b90bf8c295130/frida_tools/application.py#L547

[NSEcho]

Another great one, I did implement spawn gating in frida-go but haven't really got the change to test them out, this will be the great use case and I will get on this once I finish adding the offsets, will let you know once it is done so you can test it out.