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

tests/MyGame/Example/TestSimpleTableWithEnum.py

@@ -35,18 +35,15 @@ class TestSimpleTableWithEnum(object):
             return self._tab.Get(flatbuffers.number_types.Uint8Flags, o + self._tab.Pos)
         return 2
 
-def Start(builder): builder.StartObject(1)
-def TestSimpleTableWithEnumStart(builder):
-    """This method is deprecated. Please switch to Start."""
-    return Start(builder)
-def AddColor(builder, color): builder.PrependUint8Slot(0, color, 2)
-def TestSimpleTableWithEnumAddColor(builder, color):
-    """This method is deprecated. Please switch to AddColor."""
-    return AddColor(builder, color)
-def End(builder): return builder.EndObject()
-def TestSimpleTableWithEnumEnd(builder):
-    """This method is deprecated. Please switch to End."""
-    return End(builder)
+def TestSimpleTableWithEnumStart(builder): builder.StartObject(1)
+def Start(builder):
+    return TestSimpleTableWithEnumStart(builder)
+def TestSimpleTableWithEnumAddColor(builder, color): builder.PrependUint8Slot(0, color, 2)
+def AddColor(builder, color):
+    return TestSimpleTableWithEnumAddColor(builder, color)
+def TestSimpleTableWithEnumEnd(builder): return builder.EndObject()
+def End(builder):
+    return TestSimpleTableWithEnumEnd(builder)
 
 class TestSimpleTableWithEnumT(object):
 
@@ -74,7 +71,7 @@ class TestSimpleTableWithEnumT(object):
 
     # TestSimpleTableWithEnumT
     def Pack(self, builder):
-        Start(builder)
-        AddColor(builder, self.color)
-        testSimpleTableWithEnum = End(builder)
+        TestSimpleTableWithEnumStart(builder)
+        TestSimpleTableWithEnumAddColor(builder, self.color)
+        testSimpleTableWithEnum = TestSimpleTableWithEnumEnd(builder)
         return testSimpleTableWithEnum