fix: preserve extension of css assets in the manifest

[ElMassimo]

Description

Fixes #8764 by preserving the original extension for CSS asset entry names in the manifest.

It also preserves isEntry information for CSS asset chunks, which is useful for backend integrations.

Additional context

#6649 added assets to the manifest, but the entries are invalid for Sass/Less/Stylus stylesheets, as it's erasing the original extension from the manifest entry names and src.

What is the purpose of this pull request?

• Bug fix

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[ElMassimo]

@jessarcher @innocenzi Would you check if this commit is desirable or not?

Not sure how the Laravel plugins are using isEntry.

[innocenzi]

If I understood correctly what pure CSS chunks are, LGTM 👍

I use isEntry to know if an asset should have its own tag generated automatically (or on-demand in certain cases). I expect everything under build.rollupOptions.input to be an "isEntry" asset.

[jessarcher]

@ElMassimo This looks great, thanks!

I've tested it out with both .css and .scss files and the manifest generates as expected 👍

The official Laravel plugin isn't actually using isEntry at the moment, but I'm glad that it's there!

[patak-dev]

Thanks for the feature review and quick fix @ElMassimo!
Released in vite@3.0.0-beta.4