Enable --gen-onefile in Python (#6953)

* Enable --gen-onefile in Python

Made it possible to generate all python code in one file. Modified
py_test.py so that it can switch between the multi-file code and
the one-file code.

Updated PythonTest.sh and py_test.py so that the multi-file code
and the one-file code can be tested based on the same test code.

* Sync with google/flatbuffers

* Add --gen-onefile to generate_code.py

tests/MyGame/Example/Any.py

@@ -8,7 +8,6 @@ class Any(object):
     TestSimpleTableWithEnum = 2
     MyGame_Example2_Monster = 3
 
-
 def AnyCreator(unionType, table):
     from flatbuffers.table import Table
     if not isinstance(table, Table):

tests/MyGame/Example/AnyAmbiguousAliases.py

@@ -8,7 +8,6 @@ class AnyAmbiguousAliases(object):
     M2 = 2
     M3 = 3
 
-
 def AnyAmbiguousAliasesCreator(unionType, table):
     from flatbuffers.table import Table
     if not isinstance(table, Table):

tests/MyGame/Example/AnyUniqueAliases.py

@@ -8,7 +8,6 @@ class AnyUniqueAliases(object):
     TS = 2
     M2 = 3
 
-
 def AnyUniqueAliasesCreator(unionType, table):
     from flatbuffers.table import Table
     if not isinstance(table, Table):

tests/MyGame/Example/Color.py

@@ -10,4 +10,3 @@ class Color(object):
     Green = 2
     # \brief color Blue (1u << 3)
     Blue = 8
-

tests/MyGame/Example/Race.py

@@ -7,4 +7,3 @@ class Race(object):
     Human = 0
     Dwarf = 1
     Elf = 2
-

tests/MyGame/Example/TestEnum.py

@@ -6,4 +6,3 @@ class TestEnum(object):
     A = 0
     B = 1
     C = 2
-