testsuite: Add a repeat testcase

This test tests multiple things:

1. That huge contents are properly clipped by repeat nodes, even if the
   repeat happens in the visible part
2. That repeating only horizontally or only vertically is done quickly
   via offscreens when lots of repeating is done

testsuite/gsk/compare/repeat-repeats-nested.node

@@ -0,0 +1,14 @@
+repeat {
+  bounds: 0 0 2048 2048;
+  child: repeat {
+    bounds: 0 0 2048 2;
+    child: repeat {
+      bounds: -1 -1 2 2;
+      child: conic-gradient {
+        bounds: 0 0 32000 32000;
+        center: 16000 16000;
+        stops: 0.125 rgb(255,0,0), 0.375 rgb(0,255,0), 0.625 rgb(0,0,255), 0.875 rgb(255,255,0);
+      }
+    }
+  }
+}

testsuite/gsk/meson.build

@@ -95,6 +95,7 @@ compare_render_tests = [
   'repeat-negative-coords',
   'repeat-no-repeat',
   'repeat-repeats',
+  'repeat-repeats-nested',
   'repeat-texture',
   'repeating-gradient-scaled',
   'scale-textures-negative-ngl',