#2354 refactor `NodesOnlyMesh::ReMesh`. Pull out some methods to make it clearer what is happening, and stop making a copy of all node data and deleting it each time.

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18266 b5f69653-2bf5-0310-8201-b0dafb8e1405