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/37-floating-unmap.t

@@ -21,7 +21,7 @@ my $tmp = fresh_workspace;
 my $x = X11::XCB::Connection->new;
 
 # Create a floating window which is smaller than the minimum enforced size of i3
-my $window = open_standard_window($x, undef, 1);
+my $window = open_floating_window($x);
 ok($window->mapped, 'Window is mapped');
 
 # switch to a different workspace, see if the window is still mapped?