searchableSurface: Renamed geometry directory triSurface -> geometry

Originally the only supported geometry specification were triangulated surfaces,
hence the name of the directory: constant/triSurface, however now that other
surface specifications are supported and provided it is much more logical that
the directory is named accordingly: constant/geometry.  All tutorial and
template cases have been updated.

Note that backward compatibility is provided such that if the constant/geometry
directory does not exist but constant/triSurface does then the geometry files
are read from there.

tutorials/lagrangian/denseParticleFoam/cyclone/system/snappyHexMeshDict

@@ -78,7 +78,7 @@ castellatedMeshControls
     // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
     // Specifies a level for any cell intersected by its edges.
-    // This is a featureEdgeMesh, read from constant/triSurface for now.
+    // This is a featureEdgeMesh, read from constant/geometry for now.
     features
     (
     );