GLSL: Fix tessellation control shader bounding box support. (#1730)

Prior to this change, OES_primitive_bounding_box and EXT_primitive_bounding_box were both recognised as extensions, but only the name gl_BoundingBoxOES could be used. However the EXT version uses the name gl_BoundingBoxEXT instead. In addition, since GLES 3.2, the extension has been included in the core standard and the name gl_BoundingBox may be used instead. This change aims to make both extensions and the 3.2 core version all work.

Test/310.tesc

@@ -128,6 +128,21 @@ void goodfoop()
     d = fma(d, d, d);
 }
 
+void bbextBad()
+{
+    gl_BoundingBoxEXT;  // ERROR without GL_EXT_primitive_bounding_box
+    gl_BoundingBox;  // ERROR, version < 320
+}
+
+#extension GL_EXT_primitive_bounding_box : enable
+
+void bbext()
+{
+    gl_BoundingBoxEXT[0] = vec4(0.0);
+    gl_BoundingBoxEXT[1] = vec4(1.0);
+    gl_BoundingBoxEXT[2] = vec4(2.0);  // ERROR, overflow
+}
+
 void bbBad()
 {
     gl_BoundingBoxOES;  // ERROR without GL_OES_primitive_bounding_box