fix: asset import should skip handling data URIs

[Justineo]

Description

Vite currently transforms asset URLs inside new URL(..., import.meta.url), but if we are dealing with data URIs it incorrectly produces <some-path>/data:image/png;....

This PR made the assetImportMetaUrlPlugin skip handling data URIs and added corresponding tests.

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[hi-ogawa]

Looks good to me, thanks! I checked webpack and it looks like they also keep data url properly.

Btw, if you know it's a data url beforehand, you could simply write new URL("data:...") without import.meta.url. What's your use case you cannot do so?

[Justineo]

A dependency (built by Vite too) of the current project is producing this and I can see the vite:asset-import-meta-url plugin is transforming it to an invalid one.

[hi-ogawa]

Hmm, that's interesting. I guess we could also avoid doing that by only emitting new URL('data:...') for inlined assets as that would slightly reduce the build output. Either way, this PR should be fine as is.