gpu: ceil() offscreen size before generating offscreen

The goal is to generate an offscreen at 1x scale.
When not ceil()ing the numbers the offscreen code would do it *and*
adjust the scale accordingly, so we'd end up with something like a
1.01x scale.

And that would cause the code to reenter this codepath with the goal to
generate an offscreen at 1x scale.
And indeed, this would lead to infinite recursion.

Tests included.

Fixes #6553

gsk/gpu/gskgpunodeprocessor.c

@@ -2077,6 +2077,8 @@ gsk_gpu_node_processor_add_texture_scale_node (GskGpuNodeProcessor *self,
       /* now intersect with actual node bounds */
       if (!gsk_rect_intersection (&clip_bounds, &node->bounds, &clip_bounds))
         return;
+      clip_bounds.size.width = ceilf (clip_bounds.size.width);
+      clip_bounds.size.height = ceilf (clip_bounds.size.height);
       offscreen = gsk_gpu_node_processor_create_offscreen (self->frame,
                                                            graphene_vec2_one (),
                                                            &clip_bounds,

testsuite/gsk/compare/texture-scale-nearest-noninteger-scaled-nogl.node

@@ -0,0 +1,14 @@
+color {
+  bounds: 0 0 3 2;
+  color: rgb(0,0,0);
+}
+transform {
+  transform: scale(2);
+  child: texture-scale {
+    bounds: 0 0 1.5 1;
+    filter: nearest;
+    texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVQImWNoYGAAAAGEAIGs40g+\
+AAAAAElFTkSuQmCC\
+");
+  }
+}

testsuite/gsk/meson.build

@@ -171,6 +171,7 @@ compare_render_tests = [
   'texture-scale-filters-nocairo',
   'texture-scale-magnify-10000x',
   'texture-scale-magnify-rotate',
+  'texture-scale-nearest-noninteger-scaled-nogl',
   'texture-scale-nearest-vs-linear',
   'texture-scale-offset',
   'texture-scale-stripes',