checkMesh: Added writing of NCC coverage

If checkMesh is executed with the -allGeometry option, then surface
files containing the NCC coverage will now be written out. Coverage is
the ratio between coupled area magnitude and total area magnitude. This
is useful for locating parts of the boundary mesh that are in error.
Errors (such as folds and pinches) typically manifest as a coverage
value that deviates significantly from a value of one.

This is comparable to the writing of AMI patches's weight sums, which
also used to occur when the -allGeometry option was selected.

src/meshTools/patchToPatch/intersection/intersectionPatchToPatch.H

@@ -408,6 +408,12 @@ public:
         //- For each target face, the target and source areas for each
         //  source coupling
         inline const List<DynamicList<couple>>& tgtCouples() const;
+
+        //- Return the proportion of the source faces that are coupled
+        inline const List<scalar>& srcCoverage() const;
+
+        //- Return the proportion of the target faces that are coupled
+        inline const List<scalar>& tgtCoverage() const;
 };