ast_grep_replace: dryRun previews invalid rewrites as success; $$$ captures flatten multi-line matches #827

AFT: 0.62.0, OpenCode 2.1.4, macOS.

Two ast_grep_replace problems:

1. dryRun previews an invalid rewrite as success, while apply refuses it. Pattern foo($A, $B), rewrite bar($B, $A (unbalanced), lang: typescript, dryRun: true → "Would replace 2 match(es)" with a diff containing bar(2, 1;. Without dryRun an invalid rewrite fails with "rewritten code failed syntax validation; no files were written". The preview should run the same validation, so a preview never promises a change apply will reject.
2. Variadic captures flatten multi-line matches. Source foo(\n 3,\n 4\n);, pattern foo($$$A), rewrite bar($$$A) → bar(3,\n4); (indentation lost; dryRun and apply agree). Expected the captured nodes to keep their original separators/indentation. Relatedly ast_grep_search displays the capture as $A: 1,,,2.

Working as expected: $$$ matching, ignoring matches in strings/comments, globs and negated globs, dryRun leaving files untouched, apply matching the preview for valid rewrites.