Btag the jet: run b-tagging NNs without the BTagging object

Sometimes it would be pretty useful to use the b-tagging neural networks without a BTagging object. This MR modifies DL2Tool to add a decorate(xAOD::Jet&) method, which reads and writes auxdata to the Jet object, without requiring BTagging. The standard way to b-tag jets remains the same: the information is all added to the BTagging object via DL1Tool::decorate(xAOD::BTagging&).

So far this method isn't being used anywhere, and this addition should not change any outputs. We'd nonetheless like it to support two related applications in (b-)jet trigger:

• ATR-24308: Using tracks associated to jets to estimate the primary vertex position for that jet. With the jet vertex position we should be able to reject events where some of the leading jets are pileup, using only ROI-based tracking. Since this isn't really a b-tagging application, we should probably add any related decorations to the jet.
• We're also investigating ROI tracking for fast b-tagging. Whether the discriminant is stored on the BTagging object or the Jet object is something that we'll discuss with the jet trigger group in the coming weeks. There may be an advantage to storing on the Jet to avoid creating too many instances of BTagging (the standard b-tagging in the trigger must create a BTagging object, but runs later in the chain).