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/12-floating-resize.t

@@ -16,8 +16,7 @@ fresh_workspace;
 # Create a floating window and see if resizing works
 #####################################################################
 
-# Create a floating window
-my $window = open_standard_window($x, undef, 1);
+my $window = open_floating_window($x);
 
 # See if configurerequests cause window movements (they should not)
 my ($a, $t) = $window->rect;