glib/gpoll W32: faster GPollFD lookup

Put all ptrs for GPollFDs that contribute handles into an array, the layout of which mirrors the handles array. This way finding GPollFD for a handle is a simple matter of knowing this handle's index in the handles array (which is something we always know). Removes the need to loop through all fds looking for the right one. And, with the message FD also passed along, it's now completely unnecessary to even pass fds to poll_rest() at all.

https://bugzilla.gnome.org/show_bug.cgi?id=785468