Fix sparse_extra_3, disable counting temporaries for testing DynamicSparseMatrix.

Multiplication of column-major `DynamicSparseMatrix`es involves three
temporaries:
- two for transposing twice to sort the coefficients
(`ConservativeSparseSparseProduct.h`, L160-161)
- one for a final copy assignment (`SparseAssign.h`, L108)
The latter is avoided in an optimization for `SparseMatrix`.

Since `DynamicSparseMatrix` is deprecated in favor of `SparseMatrix`, it's not
worth the effort to optimize further, so I simply disabled counting
temporaries via a macro.

Note that due to the inclusion of `sparse_product.cpp`, the `sparse_extra`
tests actually re-run all the original `sparse_product` tests as well.

We may want to simply drop the `DynamicSparseMatrix` tests altogether, which
would eliminate the test duplication.

Related to #2048

unsupported/test/sparse_extra.cpp

@@ -22,6 +22,9 @@ static long g_dense_op_sparse_count = 0;
 #endif
 
 #define EIGEN_NO_DEPRECATED_WARNING
+// Disable counting of temporaries, since sparse_product(DynamicSparseMatrix)
+// has an extra copy-assignment.
+#define EIGEN_SPARSE_PRODUCT_IGNORE_TEMPORARY_COUNT
 #include "sparse_product.cpp"
 
 #if 0 // sparse_basic(DynamicSparseMatrix) does not compile at all -> disabled