Migrated static functions that print decls into a DeclPrinter class,

Migrated static functions that print decls into a DeclPrinter class,
which is now used (or subclasssed) by the ASTConsumers.  This new class
stores a FILE* that is used for writing, instead of just hardwiring output
to stderr (it defaults to stderr if no FILE* is provided).

Modified CreateASTPrinter() to accept a FILE* for printing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44377 91177308-0d34-0410-b5e6-96231b3b80d8