Add ps_switch_to()

[gaborcsardi]

Windows only. Switch to or send alert to the window of a process.

[gaborcsardi]

We could also have ps_find_window() (and then maybe ps_set_forground_window()`). We should also include or link to the docs at https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setforegroundwindow about the limitations for this to work.

[gaborcsardi]

This does not seem to work well enough, unfortunately.