fix(core): ensure that keep the original URL

[Cheese-Yu]

Summary

When customize html.publicPath with url and using performance.prefetch changed the parameters what I set.

Eg:
config is: publicPath: 'https://{{CDN_HOST}}/{{CDN_PATH_PREFIX}}',
output is: <link href="https://{{cdn_host}}/%7B%7BCDN_PATH_PREFIX%7D%7D/static/js/async/318.1e5b1319.js" rel="prefetch">

Because urlJoin use new URL changed url parameter.

The usage scenario is as follows:
Dynamically set CDN links when accessed by different environments.

Related Links

reproduce: https://github.com/Cheese-Yu/rsbuid-prefetch-mini-repo

Checklist

• [ x ] Tests updated (or not required).
• Documentation updated (or not required).

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[chenjiahan]

LGTM, thank you!