fix(randr): avoid querying hardware to get current configuration (#2470)

When using `get_screen_resources`, XRandR will query the hardware to
detect any change. This takes some time.
`get_screen_resources_current` uses the cached information and is
pretty fast.

In my case, the information is always already present in cache because
it was set by the program that did configure the screens (autorandr in
my case, but this applies to most frontends). As polybar is not used
to configure stuff, I think this is fine. There should be something
configuring the screen before polybar is able to use it.

However, maybe some people are using `polybar --list-monitors` just
after plugging a screen. It won't display the new screen in this case.
So, maybe this is not a good idea. It makes polybar starts
faster (500ms faster in my case when there are 3 screens plugged).
Also, I did this change because running `polybar --list-monitor` in
parallel with starting `polybar` (in a for loop for example), I get
some curious bug where my screens disappear and reappear. I don't need
this change as this was easy to fix by avoiding the parallel access to
XRandR properties, but maybe this would avoid other people running
into the same problem.

Your take!

src/x11/extensions/randr.cpp

@@ -145,7 +145,7 @@ namespace randr_util {
         primary_name = {name_iter.begin(), name_iter.end()};
       }
 
-      for (auto&& output : conn.get_screen_resources(root).outputs()) {
+      for (auto&& output : conn.get_screen_resources_current(root).outputs()) {
         try {
           auto info = conn.get_output_info(output);
           if (info->crtc == XCB_NONE) {