[browserstack benchmark tool] Use stream to write to outfile

[Linchenn]

Previously, if outfile is set and run benchmarks for multiple models, the output file records the benchmark results only for the last one model, because the program keeps overwriting the output file.

This PR:

1. Adds initialize writing and finalize writing functions for writing output files. (Adds Ctrl+C listener to make sure finalize writing function is always executed.)
2. Use JSONStream to append benchmark results whenever receiving results from BrowserStack.

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This change is 

[lina128]

Great job identifying the hard to find bug and fix it! LGTM

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055)

[pyu10055]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! 2 of 1 approvals obtained

[pyu10055]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @Linchenn)

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e2e/benchmarks/browserstack-benchmark/app.js line 400 at r1 (raw file):

  let file;
   if (cliArgs?.outfile === 'html') {
     await fs.writeFile('./benchmark_results.js', 'const a = ', 'utf8', err => {

why writing const a = to the file?

[pyu10055]

Reviewable status: complete! 2 of 1 approvals obtained

[Linchenn]

Reviewable status: complete! 2 of 1 approvals obtained

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e2e/benchmarks/browserstack-benchmark/app.js line 400 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

why writing const a = to the file?

This has been updated to const benchmarkResults = .