Add detection of browsers which cannot render correctly with diagonal

clipping regions. In this case, modify the shape of the clip region
so that it has (a number) of horizontal and vertical edges.

src/ol/reproj/Triangulation.js

@@ -337,6 +337,9 @@ class Triangulation {
     }
 
     // Exactly zero or one of *Src is not finite
+    // The triangles must have the diagonal line as the first side
+    // This is to allow easy code in reproj.s to make it straight for broken
+    // browsers that can't handle diagonal clipping
     if ((isNotFinite & 0xb) == 0) {
       this.addTriangle_(a, c, d, aSrc, cSrc, dSrc);
     }