Tpetra: Add forward declaration header files for classes
Created by: mhoemmen
@trilinos/tpetra
Users want to avoid exposure to class declarations and definitions, if they only handle classes by pointer or reference. Users also want their code to be insulated from changes to Tpetra classes' template parameters. If users make their own forward declarations of Tpetra's templated classes, those forward declarations may break if Tpetra classes' change their template parameters in ways that would otherwise not break backwards compatibility.
Tpetra should instead provide forward declaration header files for major user interface classes.