PY-71002 PEP-696: Add a set of tests that covers PEP's functionality

GitOrigin-RevId: 5d14970b62451233e8852df77a6938a18b3a17b9

python/testData/types/ClassWithDefaultGenericsDefinedInAnotherFile/mod.py

@@ -0,0 +1,6 @@
+from typing import Generic, TypeVar
+
+T = TypeVar('T', default=int)
+
+class StackOfIntsByDefault(Generic[T]):
+    def pop(self) -> T: ...

python/testData/types/ClassWithDefaultGenericsDefinedInAnotherFileAttributeAccess/mod.py

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+from typing import Generic, TypeVar
+
+T = TypeVar('T', default=int)
+U = TypeVar('U', default=str)
+
+class Box(Generic[T, U]):
+    val: T | U

python/testData/types/ClassWithDefaultGenericsDefinedInAnotherFileDefaultOverriden/mod.py

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+from typing import Generic, TypeVar
+
+T = TypeVar('T', default=int)
+
+class StackOfIntsByDefault(Generic[T]):
+    def pop(self) -> T: ...

python/testData/types/ClassWithNewStyleDefaultGenericsDefinedInAnotherFile/mod.py

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+class StackOfIntsByDefault[T = int]:
+    def pop(self) -> T: ...

python/testData/types/TypeAliasWithDefaultsDefinedInAnotherFile/mod.py

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+from typing import TypeVar, TypeAlias
+T = TypeVar('T', default = int)
+U = TypeVar('U', default = str)
+StrIntDict: TypeAlias = dict[T, U]

python/testData/types/TypeAliasWithDefaultsDefinedInAnotherFileAliasingGenericClass/mod.py

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+from typing import TypeVar, TypeAlias, Generic
+T = TypeVar('T')
+U = TypeVar('U')
+DefaultStrT = TypeVar('DefaultStrT', default = str)
+class SomethingWithNoDefaults(Generic[T, T2]): ...
+MyAlias: TypeAlias = SomethingWithNoDefaults[int, DefaultStrT]