Better python generated code naming (#6336)

* Remove a lot of redundancy from the Python generated code.

Update tutorial to reflect new Python generated code.

* Add aliases for newly deprecated Python generated methods.

This should help with backwards compatibility.

* Fix incorrect names in deprecated comments.

tests/MyGame/Example/Referrable.py

@@ -10,13 +10,17 @@ class Referrable(object):
     __slots__ = ['_tab']
 
     @classmethod
-    def GetRootAsReferrable(cls, buf, offset=0):
+    def GetRootAs(cls, buf, offset=0):
         n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
         x = Referrable()
         x.Init(buf, n + offset)
         return x
 
     @classmethod
+    def GetRootAsReferrable(cls, buf, offset=0):
+        """This method is deprecated. Please switch to GetRootAs."""
+        return cls.GetRootAs(buf, offset)
+    @classmethod
     def ReferrableBufferHasIdentifier(cls, buf, offset, size_prefixed=False):
         return flatbuffers.util.BufferHasIdentifier(buf, offset, b"\x4D\x4F\x4E\x53", size_prefixed=size_prefixed)
 
@@ -31,10 +35,18 @@ class Referrable(object):
             return self._tab.Get(flatbuffers.number_types.Uint64Flags, o + self._tab.Pos)
         return 0
 
-def ReferrableStart(builder): builder.StartObject(1)
-def ReferrableAddId(builder, id): builder.PrependUint64Slot(0, id, 0)
-def ReferrableEnd(builder): return builder.EndObject()
-
+def Start(builder): builder.StartObject(1)
+def ReferrableStart(builder):
+    """This method is deprecated. Please switch to Start."""
+    return Start(builder)
+def AddId(builder, id): builder.PrependUint64Slot(0, id, 0)
+def ReferrableAddId(builder, id):
+    """This method is deprecated. Please switch to AddId."""
+    return AddId(builder, id)
+def End(builder): return builder.EndObject()
+def ReferrableEnd(builder):
+    """This method is deprecated. Please switch to End."""
+    return End(builder)
 
 class ReferrableT(object):
 
@@ -62,7 +74,7 @@ class ReferrableT(object):
 
     # ReferrableT
     def Pack(self, builder):
-        ReferrableStart(builder)
-        ReferrableAddId(builder, self.id)
-        referrable = ReferrableEnd(builder)
+        Start(builder)
+        AddId(builder, self.id)
+        referrable = End(builder)
         return referrable