tests: lib/i3test: Remove open_standard_window, introduce open_window

open_window has a better API than open_standard_window. It uses named
parameters and supplies default values for everything you don’t specify. This
way, you can use every feature which X11::XCB::Window supports.

testcases/t/05-ipc.t

@@ -12,8 +12,7 @@ fresh_workspace;
 #####################################################################
 
 # Create a window so we can get a focus different from NULL
-my $window = open_standard_window($x);
-sync_with_i3($x);
+my $window = open_window($x);
 
 my $focus = $x->input_focus;