testsuite: Add a test for scaled texture clipping

This tests that the result is suitably clipped for doing linear
blending - the rightmost green pixel that is technically offscreen
is blending into the red pixel and turning the test yellow.

Cairo gets this wrong for some reason I didn't investigate.

testsuite/gsk/compare/scaled-texture-scale-clip-nocairo.node

@@ -0,0 +1,16 @@
+clip {
+  clip: 35 1 2 2;
+  child: color-matrix {
+    matrix: matrix3d(1000, 0, 0, 0, 0, 1000, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);
+    child: transform {
+      transform: scale(8);
+      child: texture-scale {
+        bounds: 0 0 10 10;
+        filter: nearest;
+        texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAABCAYAAAD0In+KAAAAEUlEQVQImWP4z8Dwn+E/w38AEPgD\
+/V+dao0AAAAASUVORK5CYII=\
+");
+      }
+    }
+  }
+}

testsuite/gsk/meson.build

@@ -134,6 +134,7 @@ compare_render_tests = [
   'scaled-cairo',
   'scaled-texture',
   'scaled-texture-scale',
+  'scaled-texture-scale-clip-nocairo',
   'scale0-crash',
   'shadow-behind',
   'shadow-clip-contents',