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_ast/src/node.rs

@@ -4648,6 +4648,8 @@ impl AnyNodeRef<'_> {
                 | AnyNodeRef::StmtClassDef(_)
                 | AnyNodeRef::StmtTry(_)
                 | AnyNodeRef::StmtTryStar(_)
+                | AnyNodeRef::ExceptHandlerExceptHandler(_)
+                | AnyNodeRef::ElifElseClause(_)
         )
     }