chore(html): anchor by attachment index, not by attachment type

[Skn0tt]

This PR changes how we link to an attachment element. Right now, we have &anchor=video and &anchor=diff to navigate to certain kinds of attachments. By changing this into &anchor=<attachment index>, we can make it navigate all attachments. For elements like the diff view that display data from multiple attachments, we use the smallest display attachment index as a representant.

Came out of #33267 (comment).

[github-actions]

Test results for "tests 1"

1 failed
❌ [playwright-test] › runner.spec.ts:118:5 › should ignore subprocess creation error because of SIGINT @macos-latest-node18-1

2 flaky

⚠️ [installation tests] › playwright-electron-should-work.spec.ts:44:5 › should work when wrapped inside @playwright/test and trace is enabled @package-installations-macos-latest @playwright/test
⚠️ [chromium-page] › page/page-event-popup.spec.ts:149:3 › should not treat navigations as new popups @ubuntu-20.04-chromium-tip-of-tree

36675 passed, 626 skipped
✔️✔️✔️

Merge workflow run.

[pavelfeldman]

Neither old nor new code makes much sense to me, so I might be missing something. Would it make sense to generate attachment hashes and use regular fragment navigation to reveal them?

[Skn0tt]

Would it make sense to generate attachment hashes and use regular fragment navigation to reveal them?

That was my first approach, but Dima wasn't super happy about it. Let's discuss this with the entire team.

[pavelfeldman]

Note that I changed code under your feet. As a drive-by I fixed a fairly fundamental problem where search params were not a part of the react state. Maybe it affects your implementation.

[Skn0tt]

closing in favour of #33537