Add a compare test for handling of pq colors

The node file here has a pq color that is far out of range for
sRGB, and will produce widely different result if we don't clamp
things properly.

testsuite/gsk/compare/color-pq-transparency.node

@@ -0,0 +1,4 @@
+color {
+  bounds: 0 0 50 50;
+  color: color(rec2100-pq 1 0 0 / 0.2);
+}

testsuite/gsk/meson.build

@@ -46,6 +46,7 @@ compare_render_tests = [
   'color-matrix-identity',
   'color-matrix-merge',
   'color-matrix-parsing',
+  'color-pq-transparency',
   'color-states',
   'conic-gradient-with-64-colorstops',
   'container-single-child-offscreen-for-opacity',