feat(format): skip non-plpgsql bodies; keep literals and embedded code safe

- Only restyle bodies for plpgsql/sql; skip pl* (plpython3u, plperl, ...), c and internal
- Keep LANGUAGE clause on DO blocks
- Carry multi-line string and dollar-quoted literals verbatim in bodies and DML
- Format dollar-quoted literals that contain code (declare/begin/select/...), never format() templates
- Fix code joined onto -- comments, early flush after raise exception, dropped comment before BEGIN
- Regenerate test_mm_proc golden; document in README, plan, todo

docs/plan.md

@@ -67,6 +67,9 @@ to the intended style below.
   on own line; `AS` then `$$` on its own line; body; closing `$$;` on its own line.
 - PL/pgSQL: `DECLARE` alone, vars 2-space indented; `--Block--` comment markers preserved;
   `BEGIN`/`END` at body level; `IF/THEN/ELSIF/ELSE/END IF`, loops, `CASE` indent their bodies.
+- Procedural languages: bodies in any `pl*` language other than `plpgsql` (`plpython3u`,
+  `plperl`, `pltcl`, …) and in `c` / `internal` are emitted verbatim; `plpgsql`, `sql` and routines with no `LANGUAGE` clause (treated as `sql`) are formatted. The
+  function header is always formatted.
 - Spacing: spaces around binary operators (`=`,`<>`,`||`,…) and `:=`; **no** space around
   `::`, `->`, `->>`, array `[...]`, or before a call's `(`.
 - Dollar-quote tags preserved verbatim (`$$`, `$S$`, `$Z$`, …).