fix(html): public asset urls always being treated as paths (fix #11857)

[Codex-]

Description

fix #11857

Adds a simple isUrl utility function that simply uses the node implementation of URL to validate a URL before attempting to normalize the value.

Additional context

Added tests, and I've tested this works against my issue repo with both a URL and non-url path, got the expected results.

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What is the purpose of this pull request?

• Bug fix

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[Codex-]

Unsure why the macos tests timeout, I ran the tests successfully locally on macos 🤔

[patak-dev]

Thanks for the PR @Codex-! The MacOS test was a flake, don't worry.
Would you add a test case for this one? https://github.com/vitejs/vite/blob/main/CONTRIBUTING.md#extending-the-test-suite

[Codex-]

@patak-dev really interesting test suite with playground, was interesting to dig into!

I've adapted the relative tests in assets to a new suite url, hopefully this makes sense to do.

I also validated the testing by stepping through with debugging to check we're asserting the path for a URL as expected, and explicitly so double slashes don't get broken accidentally

[Codex-]

• Rebased
• Updated added tests to match upstream move to esm

@patak-dev is there anything you want from me to get this moving? :)

[patak-dev]

Thanks for adding the tests! Sorry for the delay.
This looks good to me, we need another review now to merge it 👍🏼

[sapphi-red]

Thanks!