Insert newline after nested function or class statements (#7946)

**Summary** Insert a newline after nested function and class
definitions, unless there is a trailing own line comment.

We need to e.g. format
```python
if platform.system() == "Linux":
    if sys.version > (3, 10):
        def f():
            print("old")
    else:
        def f():
            print("new")
    f()
```
as
```python
if platform.system() == "Linux":
    if sys.version > (3, 10):

        def f():
            print("old")

    else:

        def f():
            print("new")

    f()
```
even though `f()` is directly preceded by an if statement, not a
function or class definition. See the comments and fixtures for trailing
own line comment handling.

**Test Plan** I checked that the new content of `newlines.py` matches
black's formatting.

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__function2.py.snap

@@ -73,7 +73,7 @@ with hmm_but_this_should_get_two_preceding_newlines():
  elif os.name == "nt":
      try:
          import msvcrt
-@@ -54,12 +53,10 @@
+@@ -54,7 +53,6 @@
      class IHopeYouAreHavingALovelyDay:
          def __call__(self):
              print("i_should_be_followed_by_only_one_newline")
@@ -81,11 +81,6 @@ with hmm_but_this_should_get_two_preceding_newlines():
  else:
  
      def foo():
-         pass
--
- 
- with hmm_but_this_should_get_two_preceding_newlines():
-     pass
 ```
 
 ## Ruff Output
@@ -151,6 +146,7 @@ else:
     def foo():
         pass
 
+
 with hmm_but_this_should_get_two_preceding_newlines():
     pass
 ```

crates/ruff_python_formatter/tests/snapshots/format@newlines.py.snap

@@ -7,6 +7,7 @@ input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/newlines.p
 ###
 # Blank lines around functions
 ###
+import sys
 
 x = 1
 
@@ -165,13 +166,107 @@ def f():
 # comment
 
 x = 1
-```
+
+
+def f():
+    if True:
+
+        def double(s):
+            return s + s
+    print("below function")
+    if True:
+
+        class A:
+            x = 1
+    print("below class")
+    if True:
+
+        def double(s):
+            return s + s
+        #
+    print("below comment function")
+    if True:
+
+        class A:
+            x = 1
+        #
+    print("below comment class")
+    if True:
+
+        def double(s):
+            return s + s
+    #
+    print("below comment function 2")
+    if True:
+
+        def double(s):
+            return s + s
+            #
+    def outer():
+        def inner():
+            pass
+    print("below nested functions")
+
+if True:
+
+    def double(s):
+        return s + s
+print("below function")
+if True:
+
+    class A:
+        x = 1
+print("below class")
+def outer():
+    def inner():
+        pass
+print("below nested functions")
+
+
+class Path:
+    if sys.version_info >= (3, 11):
+        def joinpath(self): ...
+
+    # The .open method comes from pathlib.pyi and should be kept in sync.
+    @overload
+    def open(self): ...
+
+
+
+
+def fakehttp():
+
+    class FakeHTTPConnection:
+        if mock_close:
+            def close(self):
+                pass
+    FakeHTTPConnection.fakedata = fakedata
+
+
+
+
+
+if True:
+    if False:
+        def x():
+            def y():
+                pass
+        #comment
+    print()
+
+
+# NOTE: Please keep this the last block in this file. This tests that we don't insert
+# empty line(s) at the end of the file due to nested function
+if True:
+    def nested_trailing_function():
+        pass```
 
 ## Output
 ```py
 ###
 # Blank lines around functions
 ###
+import sys
 
 x = 1
 
@@ -339,6 +434,118 @@ def f():
 # comment
 
 x = 1
+
+
+def f():
+    if True:
+
+        def double(s):
+            return s + s
+
+    print("below function")
+    if True:
+
+        class A:
+            x = 1
+
+    print("below class")
+    if True:
+
+        def double(s):
+            return s + s
+
+        #
+    print("below comment function")
+    if True:
+
+        class A:
+            x = 1
+
+        #
+    print("below comment class")
+    if True:
+
+        def double(s):
+            return s + s
+
+    #
+    print("below comment function 2")
+    if True:
+
+        def double(s):
+            return s + s
+            #
+
+    def outer():
+        def inner():
+            pass
+
+    print("below nested functions")
+
+
+if True:
+
+    def double(s):
+        return s + s
+
+
+print("below function")
+if True:
+
+    class A:
+        x = 1
+
+
+print("below class")
+
+
+def outer():
+    def inner():
+        pass
+
+
+print("below nested functions")
+
+
+class Path:
+    if sys.version_info >= (3, 11):
+
+        def joinpath(self):
+            ...
+
+    # The .open method comes from pathlib.pyi and should be kept in sync.
+    @overload
+    def open(self):
+        ...
+
+
+def fakehttp():
+    class FakeHTTPConnection:
+        if mock_close:
+
+            def close(self):
+                pass
+
+    FakeHTTPConnection.fakedata = fakedata
+
+
+if True:
+    if False:
+
+        def x():
+            def y():
+                pass
+
+        # comment
+    print()
+
+
+# NOTE: Please keep this the last block in this file. This tests that we don't insert
+# empty line(s) at the end of the file due to nested function
+if True:
+
+    def nested_trailing_function():
+        pass
 ```
 
 

crates/ruff_python_formatter/tests/snapshots/format@statement__if.py.snap

@@ -410,6 +410,7 @@ else:
         pass
         # 3
 
+
 if True:
     print("a")  # 1
 elif True:

crates/ruff_python_formatter/tests/snapshots/format@statement__try.py.snap

@@ -311,6 +311,7 @@ finally:
         pass
         # d
 
+
 try:
     pass  # a
 except ZeroDivisionError: