Insert empty line between suite and alternative branch after def/class (#12294)

When there is a function or class definition at the end of a suite
followed by the beginning of an alternative block, we have to insert a
single empty line between them.

In the if-else-statement example below, we insert an empty line after
the `foo` in the if-block, but none after the else-block `foo`, since in
the latter case the enclosing suite already adds empty lines.

```python
if sys.version_info >= (3, 10):
    def foo():
        return "new"
else:
    def foo():
        return "old"
class Bar:
    pass
```

To do so, we track whether the current suite is the last one in the
current statement with a new option on the suite kind.

Fixes #12199

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_formatter/tests/snapshots/black_compatibility@cases__comments9.py.snap

@@ -505,5 +505,3 @@ def foo():
 def bar():
     pass
 ```
-
-

crates/ruff_python_formatter/tests/snapshots/black_compatibility@cases__function2.py.snap

@@ -220,5 +220,3 @@ else:
 with hmm_but_this_should_get_two_preceding_newlines():
     pass
 ```
-
-

crates/ruff_python_formatter/tests/snapshots/black_compatibility@cases__stub.pyi.snap

@@ -255,5 +255,3 @@ class Conditional:
             def l(self): ...
             def m(self): ...
 ```
-
-

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

@@ -255,6 +255,68 @@ if True:
     print()
 
 
+if True:
+    def a():
+        return 1
+else:
+    pass
+
+if True:
+    # fmt: off
+    def a():
+        return 1
+    # fmt: on
+else:
+    pass
+
+match True:
+    case 1:
+        def a():
+            return 1
+    case 1:
+        def a():
+            return 1
+
+try:
+    def a():
+        return 1
+except RuntimeError:
+    def a():
+        return 1
+
+try:
+    def a():
+        return 1
+finally:
+    def a():
+        return 1
+
+try:
+    def a():
+        return 1
+except RuntimeError:
+    def a():
+        return 1
+except ZeroDivisionError:
+    def a():
+        return 1
+else:
+    def a():
+        return 1
+finally:
+    def a():
+        return 1
+
+if raw:
+    def show_file(lines):
+        for line in lines:
+            pass
+            # Trailing comment not on function or class
+
+else:
+    pass
+
+
 # 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:
@@ -558,6 +620,85 @@ if True:
     print()
 
 
+if True:
+
+    def a():
+        return 1
+else:
+    pass
+
+if True:
+    # fmt: off
+    def a():
+        return 1
+    # fmt: on
+else:
+    pass
+
+match True:
+    case 1:
+
+        def a():
+            return 1
+    case 1:
+
+        def a():
+            return 1
+
+
+try:
+
+    def a():
+        return 1
+except RuntimeError:
+
+    def a():
+        return 1
+
+
+try:
+
+    def a():
+        return 1
+finally:
+
+    def a():
+        return 1
+
+
+try:
+
+    def a():
+        return 1
+except RuntimeError:
+
+    def a():
+        return 1
+except ZeroDivisionError:
+
+    def a():
+        return 1
+else:
+
+    def a():
+        return 1
+finally:
+
+    def a():
+        return 1
+
+
+if raw:
+
+    def show_file(lines):
+        for line in lines:
+            pass
+            # Trailing comment not on function or class
+
+else:
+    pass
+
+
 # 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:
@@ -593,4 +734,63 @@ def overload4(a: int): ...
 ```
 
 
-
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -277,6 +277,7 @@
+ 
+     def a():
+         return 1
++
+ else:
+     pass
+ 
+@@ -293,6 +294,7 @@
+ 
+         def a():
+             return 1
++
+     case 1:
+ 
+         def a():
+@@ -303,6 +305,7 @@
+ 
+     def a():
+         return 1
++
+ except RuntimeError:
+ 
+     def a():
+@@ -313,6 +316,7 @@
+ 
+     def a():
+         return 1
++
+ finally:
+ 
+     def a():
+@@ -323,18 +327,22 @@
+ 
+     def a():
+         return 1
++
+ except RuntimeError:
+ 
+     def a():
+         return 1
++
+ except ZeroDivisionError:
+ 
+     def a():
+         return 1
++
+ else:
+ 
+     def a():
+         return 1
++
+ finally:
+ 
+     def a():
+```

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

@@ -160,11 +160,17 @@ def f():
     pass
 
 
+if True:
+    def a():
+        return 1
+else:
+    pass
 
 
 # comment
 
 x = 1
+
 ```
 
 ## Output
@@ -302,10 +308,28 @@ x = 1
 def f():
     pass
 
+if True:
+    def a():
+        return 1
+else:
+    pass
+
 # comment
 
 x = 1
 ```
 
 
-
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -134,6 +134,7 @@
+ if True:
+     def a():
+         return 1
++
+ else:
+     pass
+ 
+```

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

@@ -1042,3 +1042,26 @@ def func[T](
     lotsoflongargs5: T,
 ) -> T: ...
 ```
+
+
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -161,6 +161,7 @@
+ 
+     def f1():
+         pass  # a
++
+ else:
+     pass
+ 
+@@ -170,6 +171,7 @@
+     def f2():
+         pass
+         # a
++
+ else:
+     pass
+ 
+```

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

@@ -609,4 +609,22 @@ if parent_body:
 ```
 
 
-
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -93,11 +93,13 @@
+     def f():
+         pass
+         # 1
++
+ elif True:
+ 
+     def f():
+         pass
+         # 2
++
+ else:
+ 
+     def f():
+```

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

@@ -366,4 +366,28 @@ finally:
 ```
 
 
-
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -117,16 +117,19 @@
+     def f():
+         pass
+         # a
++
+ except:
+ 
+     def f():
+         pass
+         # b
++
+ else:
+ 
+     def f():
+         pass
+         # c
++
+ finally:
+ 
+     def f():
+```

crates/ruff_python_formatter/tests/snapshots/format@stub_files__blank_line_after_nested_stub_class.pyi.snap

@@ -414,6 +414,3 @@ class Eof:
     class Nested:
         pass
 ```
-
-
-

crates/ruff_python_formatter/tests/snapshots/format@stub_files__suite.pyi.snap

@@ -311,4 +311,24 @@ class ComplexStatements:
 ```
 
 
-
+## Preview changes
+```diff
+--- Stable
++++ Preview
+@@ -132,6 +132,7 @@
+     if sys.version_info >= (3, 12):
+         @classmethod
+         def fromtimestamp(cls, timestamp: float, tz: float | None = ...) -> Self: ...
++
+     else:
+         @classmethod
+         def fromtimestamp(cls, __timestamp: float, tz: float | None = ...) -> Self: ...
+@@ -141,6 +142,7 @@
+     if sys.version_info >= (3, 8):
+         @classmethod
+         def now(cls, tz: float | None = None) -> Self: ...
++
+     else:
+         @classmethod
+         def now(cls, tz: None = None) -> Self: ...
+```