gh-157003: Add flush() method to HTMLParser.

[ianjosephwilson]

• Add flush() method to HTMLParser
  • Add docstring
  • Add test
  • Add blurb
• Small fix to HTMLParser's EventCollector test fixture

• Issue: Add flush() to HTMLParser to fill gap after implementation change #157003

[python-cla-bot]

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Documentation build overview

📚 cpython-previews | 🛠️ Build #34412104 | 📁 Comparing b06b12e against main (7a91841)

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2 files changed

± library/html.parser.html
± whatsnew/changelog.html

[ianjosephwilson]

Please note that the "fix" in 70db209 is slightly out of scope but prevented re-invoking get_events() during a test run.