TauAnalysisTools: Lock decorations produced by TauTruthMatchingTool.

As part of fixing the race condition with decorations and deep copies, we need to ensure that decorations get locked after they're written. TauAnalysisTools was attaching decorations using SG::Decorator and not locking them.

Since the interfaces of TauAnalysisTools take one tau object at a time (and this wasn't straightforward to change), we do this by adding a new interface to create an object containing the needed WriteDecorHandles. This then gets passed to the methods that add decorations, and it should be destroyed after all tau objects are processed.

See ATLASRECTS-8008.