swift234

[AST] Formatting consistency in conditional compilation output

Before:
```
(#if_stmt
  (#if:
    (stuff)     #else
    (stuff))
```

After:
```
(#if_stmt
  (#if:
    (stuff))
  (#else:
    (stuff)))
```

Notable differences:
 - #if block is closed
 - #else block is treated same as #if block, starts on new line, token terminated with `:`
 - #else block is closed