Revert "Cleanup: use regular templates in .tcc for Attribute, Variable"
Created by: williamfgc
Reverts ornladios/ADIOS2#1225
Reverting as the current structure doesn't allow separating functions that only apply to specific types.
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Created by: williamfgc
Reverts ornladios/ADIOS2#1225
Reverting as the current structure doesn't allow separating functions that only apply to specific types.