[url_launcher] fix: tab traversal on web

[pedromassango]

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

Continuation of #9815

Fixes flutter/flutter#157689

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[gemini-code-assist]

Code Review

This pull request fixes an accessibility issue in url_launcher_web where the Link widget created duplicate semantic nodes. The change wraps the existing Semantics widget in _buildChild with a MergeSemantics widget to combine the semantic information of the link and its child. A new integration test has been added to verify that a MergeSemantics widget is present in the widget tree for a WebLinkDelegate. The package version has been bumped to 2.4.2 and the CHANGELOG.md has been updated to reflect this fix. My review includes a suggestion to align the new changelog entry with the repository's style guide.

[pedromassango]

@chunhtai I was expecting this test to fail as the engine fix landed already 🤔

I mean now that the engine prioritize link, then ideally this test don't need isButton: true right? Are the tests not being ran against the master branch of the flutter?

[mdebbar]

I think tests run against master AND stable (@stuartmorgan-g to confirm).

If this code is expected to work with master but not with stable, then you need to wait until your flutter fix makes it to stable.

[stuartmorgan-g]

Most tests (including web integration tests) are run against master and stable, yes.

[pedromassango]

@mdebbar I believe it should be fine now since all tests are passing (had to update some existing ones to align with the new behavior)

My comment above (here) is really just a curiosity, as per my understanding after my engine fix, then ideally no isButton should be expeted

[stuartmorgan-g]

I believe it should be fine now since all tests are passing

If a test that you expected to fail is passing, that doesn't sound fine; it sounds like there's a potential test issue here that should be investigated. Am I misunderstanding?

[mdebbar]

Reading the previous (reverted) PR:

With MergeSemantics, the semantics tree was not generated properly, e.g linkUrl value gets removed from the final semantics tree. This is being fixed in the engine, see flutter/flutter#174473

That sounds like we need to wait until the engine fix lands in stable.

[pedromassango]

Am I misunderstanding?

I would say no, but, I'm only 50% sure about my statement and that is why I am looking for @chunhtai 's feedback as he has way more knowledge on this.

But yes, from my understanding, that test should fail as my engine fix now prioritize the link flag over the button one, meaning isButton: true should make it fail.

Anyway, will wait for the fix to land on stable and then, expectt the test to fail

[stuartmorgan-g]

Anyway, will wait for the fix to land on stable and then, expectt the test to fail

The test passed CI on master, pinned to 8d0b31d81a02d13ee37d17c9387d7bbcd1c2baba (which is yesterday), so it's not clear to me what reason there would be to expect different results when the current master reaches stable.