Treating NoneType as None and warning against using NoneType. (#13153)

### Description

Fixes #11288

Warns people to not use `NoneType` as a type annotation, as requested in #11288.

### Example

**Before**

```python
from types import NoneType

def f(x: NoneType) -> None:
    pass

f(None) # E: Argument 1 to "f" has incompatible type "None"; expected "NoneType"
```

**After**

```python
from types import NoneType

def f(x: NoneType) -> None: # E: NoneType should not be used as a type, please use None instead 
    pass

f(None)
```

Had to edit `test-data/unit/lib-stub/types.pyi` to allow NoneType type annotation.

mypy/typeanal.py

@@ -508,6 +508,11 @@ def analyze_type_with_type_info(
  # Create a named TypedDictType
  return td.copy_modified(item_types=self.anal_array(list(td.items.values())),
  fallback=instance)
+
+ if info.fullname == 'types.NoneType':
+ self.fail("NoneType should not be used as a type, please use None instead", ctx)
+ return NoneType(ctx.line, ctx.column)
+
  return instance
 
  def analyze_unbound_type_without_type_info(self, t: UnboundType, sym: SymbolTableNode,

test-data/unit/check-python310.test

@@ -1591,3 +1591,12 @@ def test_func(test_str: str) -> str:
  return "special"
  case _:
  return "other"
+
+
+[case testNoneTypeWarning]
+from types import NoneType
+
+def foo(x: NoneType): # E: NoneType should not be used as a type, please use None instead
+ reveal_type(x) # N: Revealed type is "None"
+
+[builtins fixtures/tuple.pyi]

test-data/unit/lib-stub/types.pyi

@@ -11,3 +11,6 @@ class ModuleType:
 if sys.version_info >= (3, 10):
  class Union:
  def __or__(self, x) -> Union: ...
+
+ class NoneType:
+ ...