Pr introduces sanitizing of the adapter... names in the oneOf and anyOf model templates in order to avoid incorrect names being generated.
The root cause of this issue comes from the fact that Kotlin generator uses canonical names for type mappings and thus {{dataType}} variable is a canonical name with dots. It is then used for variable names generation.
Sanitizing of the names will be enough to fix #19942 but the type mappings problem should also be addressed imo.
It seems that other generators (i.e. java) are not having this issue.

During the preparation of this fix, I also realized that validateJsonElement methods are also missing in oneOf and anyOf classes, which would also cause the compilation errors. I fixed this issue as well in the scope of this pr.

Technical Kotlin Committee:
@dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m @stefankoppier @e5l

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