This PR adds a check for `build.rollupOptions.input` in addition to
`build.rollupOptions.inputs`. Plugins like `sveltekit()` will use the
former property, and we should infer build/server targets correctly in
those cases.
## Current Behavior
`sveltekit()` is not supported
## Expected Behavior
`sveltekit()` and other setups using `input` are supported
## Related Issue(s)
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merged. -->
Fixes #
412dade3b7