Use replace history handling for same-URL browser UI navigations

[shannonbooth]

Fixes: #12803

• At least two implementers are interested (and none opposed):
  • Chrome: Already implements
  • Gecko: Based on comments under Should a same URL navigation from browser UI be a replace? #12803,considered bug
  • Safari:
• Tests are written and can be reviewed and commented upon at:
  • [webdriver] Test same-URL navigation replaces the current history entry web-platform-tests/wpt#62160
  • NB on the test above, this makes some assumptions about how webdriver integrates to HTML spec. But I dont think this can be tested otherwise as far as I know.
• Implementation bugs are filed:
  • Chromium: N/A, already implemented
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=2067459
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=322863
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A
• MDN issue is filed: N/A
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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/browsing-the-web.html ( diff )

[whimboo]

Hi @shannonbooth. Is this PR ready for review? If yes, we might have to find one or more folks to review it. Right now no-one is actually assigned. I'ld like to wait with the review of the wpt test additions for WebDriver until this PR is ready to get merged. Thanks.