Support storage of output from "MAP_INPUT" functor that returns "std::optional<T>" or "std::nullopt"

Abhijit Mathad requested to merge AM_mc_association into master

This MR supports storage of output of MAP_INPUT functor that returns std::optional<T> or std::nullopt. In this regard, it adds a helper class LHCb::FTuple::InvalidValue to store default (invalid) value when std::nullopt is returned. Idea arose from discussions with @graven in this MR `(Rec!2666 (closed)) (particularly in this comment).

Also support tupling of SIMDWrapper::scalar::float_v, avoid explicit std::any declaration, fix to fill_ method of non-symmetric matrices and clean-up obsolete header file inclusion.

This MR is related to (but not dependent on): Rec!2666 (closed)

FYI: @graven , @mferrill and @powen

Edited by Abhijit Mathad

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