Auto merge of #14122 - glennw:update-wr-subpx, r=emilio

Update WR and shaders (initial subpixel AA work).

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resources/shaders/ps_text_run.fs.glsl

@@ -3,6 +3,9 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 void main(void) {
+#ifdef WR_FEATURE_SUBPIXEL_AA
+    oFragColor = texture(sDiffuse, vUv);
+#else
     float a = texture(sDiffuse, vUv).a;
 #ifdef WR_FEATURE_TRANSFORM
     float alpha = 0.0;
@@ -10,4 +13,5 @@ void main(void) {
     a *= alpha;
 #endif
     oFragColor = vec4(vColor.rgb, vColor.a * a);
+#endif
 }