Add strategy alias for execution_strategy in FieldResolutionContext
Add strategy alias for execution_strategy in FieldResolutionContext

This is for backwards compatiblity so graphql-batch doesn't need to only
support older or newer versions of the graphql gem.

rmosolgo/graphql-ruby,nevesenin/graphql-ruby,xuorig/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby,nevesenin/graphql-ruby,rmosolgo/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby,xuorig/graphql-ruby,xuorig/graphql-ruby