A number of pile-up tools (in
MuonSpectrometer) weren't clonable because they contained
ReadHandleKeys that were reset on initialization, which broke when there were multiple instances of the tool.
This MR turns those properties into
StringProperties and initializes the
ReadHandleKey from the
StringProperty if necessary. The
ReadHandleKey is still exposed as a (renamed) property but does not need to be set in any configuration.