xAODForward: A few fixes/tweaks to the dictionaries/classes

As discussed in ATLASRECTS-6972, this MR tweaks some of the class definitions in the xAODForward package. In a nutshell, hardcoded version numbers are dropped from the ElementLinks such they we always refer to the most up-to-date version through typedefs. This way, we'll always be referring to the current version automatically.

Let me explicitly tag @pbalek and @akraszna to make sure that I'm not missing anything obvious w/ this one. In principle, the change should be transparent.

PS: We also fix an inconsistency in the header/cmake files (see ATR-25342), which was causing auto-parsing (hence costing us memory).