gh-156810: Write the profiler's collapsed-stack export as UTF-8

[tonghuaroot]

CollapsedStackCollector.export opened its output file with open(filename, "w") — the only exporter in stack_collector.py without an explicit encoding= (the flamegraph, JSONL and heatmap exporters all pass encoding="utf-8"). Since the collapsed format writes frame names verbatim, it crashed with UnicodeEncodeError on non-ASCII frame names under a non-UTF-8 locale, and on surrogate-escaped filenames on any locale.

Open the file as UTF-8 with errors="surrogatepass": utf-8 matches the sibling exporters, and surrogatepass is needed because — unlike the json-based exporters, which escape via ensure_ascii — collapsed writes names verbatim and frame filenames can be surrogate-escaped (undecodable paths).

The added test fails without the fix; test_profiling passes.

• Issue: profiling: --collapsed export crashes with UnicodeEncodeError on non-ASCII frame names #156810

[pablogsal]

Thanks a lot for the fix!

[miss-islington-app]

Thanks @tonghuaroot for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-156814 is a backport of this pull request to the 3.15 branch.