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/61-regress-borders-restart.t

@@ -12,7 +12,7 @@ use i3test;
 my $x = X11::XCB::Connection->new;
 my $i3 = i3(get_socket_path());
 my $tmp = fresh_workspace;
-my $window = open_standard_window($x);
+my $window = open_window($x);
 
 sub get_border_style {
     my @content = @{get_ws_content($tmp)};