multi-texture-format: Use BT709 coefficients in the YUV shader

In order to be consistent with KMS, i.e. avoid noticable color changes when
switching between hardware plane offloading and compositing.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4204>

src/compositor/meta-multi-texture-format.c

@@ -32,9 +32,9 @@ static const char *shader_global_conversions =
   "  float Y = 255.0/219.0 * (yuva.x - 16.0/255.0);                         \n"
   "  float su = yuva.y - 128.0/255.0;                                       \n"
   "  float sv = yuva.z - 128.0/255.0;                                       \n"
-  "  res.r = Y                   + 1.59602678 * sv;                         \n"
-  "  res.g = Y - 0.39176229 * su - 0.81296764 * sv;                         \n"
-  "  res.b = Y + 2.01723214 * su;                                           \n"
+  "  res.r = Y                   + 1.79274107 * sv;                         \n"
+  "  res.g = Y - 0.21324861 * su - 0.53290933 * sv;                         \n"
+  "  res.b = Y + 2.11240179 * su;                                           \n"
   "  res.rgb *= yuva.w;                                                     \n"
   "  res.a = yuva.w;                                                        \n"
   "  return res;                                                            \n"