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/resources/test/fixtures/ruff/statement/class_definition.py

@@ -35,5 +35,11 @@ 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
+
+

crates/ruff_python_formatter/resources/test/fixtures/ruff/statement/if.py

@@ -88,13 +88,17 @@ 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

crates/ruff_python_formatter/resources/test/fixtures/ruff/statement/try.py

@@ -106,16 +106,35 @@ 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