Modernize WritePackedDst

• prefer Gaudi::Functional::MergingTransformer
• make thread-safe: move datamembers to PackedDst struct
• add 'add(const T&)' members to PackedDst struct for all known types
• replace the big if-then-else-if-then construct with a fold expression over the listed types, which dynamic_casts to the matching type, and then calls one of the provided overloads

added backport run2 modernisation labels

added 1 commit

• eeb0bd46 - Modernize WritePackedDst

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/ci-test --merge

assigned to @mstahl

resolved all threads

added lhcb-gaudi-head label

approved this merge request

added 1 deleted label and removed backport run2 modernisation labels

assigned to @rmatev and unassigned @mstahl

added backport run2 modernisation labels and removed lhcb-gaudi-head label

mentioned in merge request !2290 (merged)

removed 1 deleted label

mentioned in issue Moore#128 (closed)

@graven by "sits on top of" do you mean "depends on" and/or "should be tested with" !2297 (merged)? :)

It literally 'sits on top of' !2297 (merged), i.e. this MR consists of two commits, the first of which is !2297 (merged). So if !2297 (merged) is merged prior to this one, the 'diff' for this MR becomes a lot smaller. On the other hand, if this one is merged, than !2297 (merged) gets implicitly & automatically merged as well.

mentioned in issue Moore#131 (closed)

added lhcb-gaudi-head label

The nightlies seemed generally happy with all these modernisations that I had marked as ready, except it failed to merge in this one, see: https://lhcb-nightlies.web.cern.ch/logs/checkout/nightly/lhcb-gaudi-head/2522/LHCb/. It looks like conflicts with !2297 (merged) if I read the log right. So perhaps we merge !2297 (merged) first (along with all the others - !2293 (merged), !2299 (merged), Lbcom!400 (merged), Lbcom!402 (merged), Lbcom!411 (merged) and Lbcom!412 (merged)) and then stick this MR in tonight's nightlies. @rmatev does this sensible?

removed lhcb-gaudi-head label

@jonrob: could you please take a look at this, and if you are OK with it hit the 'approve' button?