console.lua: add a keep_open flag to mp.input

With input.select this allows building nested submenus without the flicker of console quickly closing and reopening, and also doing multiple selections, to e.g. cycle through different values of a property, or increase a property multiple times. With input.get this is used to change the default behavior to closing by default on submit. It was argued by avih that this is more useful, and indeed Github code search shows that everybody is calling input.terminate() unconditionally on submit, so the impact of the change should be low, and restoring the old behavior is as easy as passing keep_open = true, which is just ignored in older mpv versions.

GCGuido Cella committed 1 year ago