Rename runtime2 test files and make runtime2 tests round-trip

Rename all runtime2 test files to have names like test.dat for test data files and test.dat.xml for test infoset files. Simplify runtime2 TDML test cases by enabling round-tripping, merging pairs of parser test cases and unparser test cases, and removing unneeded attributes (description, root). Fix problem found in Runtime2TDMLDFDLProcessor after enabling round-tripping.