Keep methods with struct name and switch them to default (#6879)

* Keep methods with struct name and switch them to default

This PR can help fix the following two issues:
1): A set of simplified API (without struct name) was added in
https://github.com/google/flatbuffers/pull/6336. It causes name
conflict when merging all generated python file into a single one
(the primary usage senario in Google).
2): Flatbuffers 2.0 generates absolute import path, which may cause
name space conflicts. See more details in
https://github.com/google/flatbuffers/issues/5840.

The solution for both is to generate the merged Python code, similar
C++. The merged code will not contain the simplied API, but only the
method with struct name. For issue (1), it will mimic the exactly
usage pattern for Google internal. For issue (2), users can generate
the merged flatbuffer code, without worrying about the imports.

The above idea will be implemented in the following steps:
Step 1 (this PR): revert changes in https://github.com/google/flatbuffers/pull/6336
that set the simplified API as default. Remove statements that the
original API will be deprecated, and reset the original API as default.
Step 2 (the following PR): create a flag to generate the merged code.
The Simplified API will be removed from the merged code, otherwise it
will cause name conflict.

* Update the generated sample code

* Update the generated example code

* Reverst the changes of GetRootAs

* Update examples from grpc/example/generate.sh

grpc/examples/python/greeter/models/HelloReply.py

@@ -31,15 +31,12 @@ class HelloReply(object):
             return self._tab.String(o + self._tab.Pos)
         return None
 
-def Start(builder): builder.StartObject(1)
-def HelloReplyStart(builder):
-    """This method is deprecated. Please switch to Start."""
-    return Start(builder)
-def AddMessage(builder, message): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(message), 0)
-def HelloReplyAddMessage(builder, message):
-    """This method is deprecated. Please switch to AddMessage."""
-    return AddMessage(builder, message)
-def End(builder): return builder.EndObject()
-def HelloReplyEnd(builder):
-    """This method is deprecated. Please switch to End."""
-    return End(builder)
+def HelloReplyStart(builder): builder.StartObject(1)
+def Start(builder):
+    return HelloReplyStart(builder)
+def HelloReplyAddMessage(builder, message): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(message), 0)
+def AddMessage(builder, message):
+    return HelloReplyAddMessage(builder, message)
+def HelloReplyEnd(builder): return builder.EndObject()
+def End(builder):
+    return HelloReplyEnd(builder)

grpc/examples/python/greeter/models/HelloRequest.py

@@ -31,15 +31,12 @@ class HelloRequest(object):
             return self._tab.String(o + self._tab.Pos)
         return None
 
-def Start(builder): builder.StartObject(1)
-def HelloRequestStart(builder):
-    """This method is deprecated. Please switch to Start."""
-    return Start(builder)
-def AddName(builder, name): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(name), 0)
-def HelloRequestAddName(builder, name):
-    """This method is deprecated. Please switch to AddName."""
-    return AddName(builder, name)
-def End(builder): return builder.EndObject()
-def HelloRequestEnd(builder):
-    """This method is deprecated. Please switch to End."""
-    return End(builder)
+def HelloRequestStart(builder): builder.StartObject(1)
+def Start(builder):
+    return HelloRequestStart(builder)
+def HelloRequestAddName(builder, name): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(name), 0)
+def AddName(builder, name):
+    return HelloRequestAddName(builder, name)
+def HelloRequestEnd(builder): return builder.EndObject()
+def End(builder):
+    return HelloRequestEnd(builder)