Rewrite placement logic (#6040)

## Summary
This is a rewrite of the main comment placement logic. `place_comment`
now has three parts:

- place own line comments
  - between branches
  - after a branch
- place end-of-line comments
  - after colon
  - after a branch
- place comments for specific nodes (that include module level comments)

The rewrite fixed three bugs: `class A: # trailing comment` comments now
stay end-of-line, `try: # comment` remains end-of-line and deeply
indented try-else-finally comments remain with the right nested
statement.

It will be much easier to give more alternative branches nodes since
this is abstracted away by `is_node_with_body` and the first/last child
helpers. Adding new node types can now be done by adding an entry to the
`place_comment` match. The code went from 1526 lines before #6033 to
1213 lines now.

It thinks it easier to just read the new `placement.rs` rather than
reviewing the diff.

## Test Plan

The existing fixtures staying the same or improving plus new ones for
the bug fixes.

crates/ruff_python_formatter/tests/snapshots/black_compatibility@simple_cases__fmtskip8.py.snap

@@ -74,7 +74,7 @@ async def test_async_with():
 ```diff
 --- Black
 +++ Ruff
-@@ -1,62 +1,63 @@
+@@ -1,62 +1,62 @@
  # Make sure a leading comment is not removed.
 -def some_func(  unformatted,  args  ):  # fmt: skip
 +def some_func(unformatted, args):  # fmt: skip
@@ -134,15 +134,13 @@ async def test_async_with():
  
  
 -try  :  # fmt: skip
-+try:
-+    # fmt: skip
++try:  # fmt: skip
      some_call()
 -except  UnformattedError  as  ex:  # fmt: skip
--    handle_exception()
--finally  :  # fmt: skip
 +except UnformattedError as ex:  # fmt: skip
-+    handle_exception()  # fmt: skip
-+finally:
+     handle_exception()
+-finally  :  # fmt: skip
++finally:  # fmt: skip
      finally_call()
  
  
@@ -207,12 +205,11 @@ async def test_async_for():
         print("Do something")
 
 
-try:
-    # fmt: skip
+try:  # fmt: skip
     some_call()
 except UnformattedError as ex:  # fmt: skip
-    handle_exception()  # fmt: skip
-finally:
+    handle_exception()
+finally:  # fmt: skip
     finally_call()
 
 

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

@@ -32,14 +32,12 @@ def h():
 ```diff
 --- Black
 +++ Ruff
-@@ -1,18 +1,26 @@
+@@ -1,18 +1,25 @@
  def f():  # type: ignore
      ...
  
--class x:  # some comment
 +
-+class x:
-+    # some comment
+ class x:  # some comment
      ...
  
 -class y: ...  # comment
@@ -71,8 +69,7 @@ def f():  # type: ignore
     ...
 
 
-class x:
-    # some comment
+class x:  # some comment
     ...
 
 

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

@@ -41,8 +41,14 @@ class Test(aaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbb + cccccccccccccccccccccccc +
 class Test(aaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbbbbb * cccccccccccccccccccccccc + dddddddddddddddddddddd + eeeeeeeee, ffffffffffffffffff, gggggggggggggggggg):
     pass
 
-class Test(Aaaa): # trailing comment
+class TestTrailingComment1(Aaaa): # trailing comment
     pass
+
+
+class TestTrailingComment2: # trailing comment
+    pass
+
+
 ```
 
 ## Output
@@ -102,7 +108,11 @@ class Test(
     pass
 
 
-class Test(Aaaa):  # trailing comment
+class TestTrailingComment1(Aaaa):  # trailing comment
+    pass
+
+
+class TestTrailingComment2:  # trailing comment
     pass
 ```
 

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

@@ -94,13 +94,17 @@ def f():
         # comment
 
 if True:
-    def f2():
+    def f():
         pass
         # 1
-else:
-    def f2():
+elif True:
+    def f():
         pass
         # 2
+else:
+    def f():
+        pass
+        # 3
 
 if True: print("a") # 1
 elif True: print("b") # 2
@@ -199,13 +203,17 @@ def f():
 
 
 if True:
-    def f2():
+    def f():
         pass
         # 1
-else:
-    def f2():
+elif True:
+    def f():
         pass
         # 2
+else:
+    def f():
+        pass
+        # 3
 
 if True:
     print("a")  # 1

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

@@ -112,19 +112,38 @@ except RuntimeError:
     raise
 
 try:
-    def f2():
+    def f():
         pass
         # a
 except:
-    def f2():
+    def f():
         pass
         # b
+else:
+    def f():
+        pass
+        # c
+finally:
+    def f():
+        pass
+        # d
 
 try: pass # a
 except ZeroDivisionError: pass # b
-except: pass # b
+except: pass # c
 else: pass # d
-finally: pass # c
+finally: pass # e
+
+try:  # 1 preceding: any, following: first in body, enclosing: try
+    print(1)  # 2 preceding: last in body, following: fist in alt body, enclosing: try
+except ZeroDivisionError:  # 3 preceding: test, following: fist in alt body, enclosing: try
+    print(2)  # 4 preceding: last in body, following: fist in alt body, enclosing: exc
+except:  # 5 preceding: last in body, following: fist in alt body, enclosing: try
+    print(2)  # 6 preceding: last in body, following: fist in alt body, enclosing: exc
+else:  # 7 preceding: last in body, following: fist in alt body, enclosing: exc
+    print(3)  # 8 preceding: last in body, following: fist in alt body, enclosing: try
+finally:  # 9 preceding: last in body, following: fist in alt body, enclosing: try
+    print(3)  # 10 preceding: last in body, following: any, enclosing: try
 ```
 
 ## Output
@@ -140,8 +159,7 @@ except KeyError:  # should remove brackets and be a single line
     ...
 
 
-try:
-    # try
+try:  # try
     ...
     # end of body
 # before except
@@ -160,8 +178,7 @@ finally:
 
 
 # with line breaks
-try:
-    # try
+try:  # try
     ...
     # end of body
 
@@ -213,8 +230,7 @@ except:
 
 
 # try/except*, mostly the same as try
-try:
-    # try
+try:  # try
     ...
     # end of body
 # before except
@@ -247,24 +263,43 @@ except RuntimeError:
     raise
 
 try:
-    def f2():
+    def f():
         pass
         # a
 except:
-    def f2():
+    def f():
         pass
         # b
+else:
+    def f():
+        pass
+        # c
+finally:
+    def f():
+        pass
+        # d
 
 try:
     pass  # a
 except ZeroDivisionError:
     pass  # b
 except:
-    pass  # b
+    pass  # c
 else:
     pass  # d
 finally:
-    pass  # c
+    pass  # e
+
+try:  # 1 preceding: any, following: first in body, enclosing: try
+    print(1)  # 2 preceding: last in body, following: fist in alt body, enclosing: try
+except ZeroDivisionError:  # 3 preceding: test, following: fist in alt body, enclosing: try
+    print(2)  # 4 preceding: last in body, following: fist in alt body, enclosing: exc
+except:  # 5 preceding: last in body, following: fist in alt body, enclosing: try
+    print(2)  # 6 preceding: last in body, following: fist in alt body, enclosing: exc
+else:  # 7 preceding: last in body, following: fist in alt body, enclosing: exc
+    print(3)  # 8 preceding: last in body, following: fist in alt body, enclosing: try
+finally:  # 9 preceding: last in body, following: fist in alt body, enclosing: try
+    print(3)  # 10 preceding: last in body, following: any, enclosing: try
 ```