execute: move publishing code into separate file

Replicates graphql/graphql-js@04e948b

Author: Cito

docs/conf.py

@@ -165,10 +165,11 @@
 graphql.execution.collect_fields.FieldsAndPatches
 graphql.execution.map_async_iterable.map_async_iterable
 graphql.execution.Middleware
-graphql.execution.execute.DeferredFragmentRecord
 graphql.execution.execute.ExperimentalIncrementalExecutionResults
 graphql.execution.execute.StreamArguments
-graphql.execution.execute.StreamItemsRecord
+graphql.execution.incremental_publisher.IncrementalPublisherMixin
+graphql.execution.incremental_publisher.StreamItemsRecord
+graphql.execution.incremental_publisher.DeferredFragmentRecord
 graphql.language.lexer.EscapeSequence
 graphql.language.visitor.EnterLeaveVisitor
 graphql.type.definition.TContext

src/graphql/execution/__init__.py

@@ -17,17 +17,19 @@
     ExecutionResult,
     ExperimentalIncrementalExecutionResults,
     InitialIncrementalExecutionResult,
-    SubsequentIncrementalExecutionResult,
-    IncrementalDeferResult,
-    IncrementalStreamResult,
-    IncrementalResult,
     FormattedExecutionResult,
     FormattedInitialIncrementalExecutionResult,
+    Middleware,
+)
+from .incremental_publisher import (
     FormattedSubsequentIncrementalExecutionResult,
     FormattedIncrementalDeferResult,
-    FormattedIncrementalStreamResult,
     FormattedIncrementalResult,
-    Middleware,
+    FormattedIncrementalStreamResult,
+    IncrementalDeferResult,
+    IncrementalResult,
+    IncrementalStreamResult,
+    SubsequentIncrementalExecutionResult,
 )
 from .async_iterables import map_async_iterable
 from .middleware import MiddlewareManager