introduce new execute exports #4215
                
     Merged
            
            
          
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operating on
ValidatedExecutionArguments:executeQueryOrMutationOrSubscriptionEvent()andexperimentalExecuteQueryOrMutationOrSubscriptionEvent()motivation: allows library users/servers to make sure that documents contain necessary operation and that variables coerce, and then allow them to call an executor on those already validated arguments
motivation: missing piece necessary for really closing #3679