moved from the field attribute declaration and created a placeholder
which then is resolved in the field attribute class.
this is to avoid unwanted persistent of the defaults across objects which introduces
stealth bugs when multiple objects of the same kind are used in succession while
not overriding the default values.
FieldAttributes will now by default not be post_validated unless a flag
is set on them in the class, as a large number of fields are really there
simply to be inherited by Task/PlayContext and shouldn't be templated too
early.
The other (unrelated to the base issue) in #12084 is also fixed here, where
the roles field is loaded before vars/vars_files, meaning there are no vars
yet loaded in the play when the templating occurs.
Fixes#12084
