feat(oxfmt): add insert_final_newline option

[Boshen]

closes #15066

The difficult part here is only calculate line ending at the really end, just before write, to avoid memory allocations on the source text when you insert a newline.

@leaysgur This feature also requires a single file formatter so we can apply this to node API and file system write. The single file formatter need to accept a Writer so we can write to string or file.

[codspeed-hq]

CodSpeed Performance Report

Merging #16757 will not alter performance

_{Comparing 12-11-feat_oxfmt_add_insert_final_newline_option (e849aaf) with main (083e081)¹}

Summary

✅ 30 untouched
⏩ 15 skipped²

Footnotes

1. No successful run was found on main (2acd66e) during the generation of this report, so 083e081 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 15 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩