Fix React dev mode using a base

[matthewp]

Changes

• React Refresh is the module @react-refresh. Previously we were loading it as /basepathname/@react-refresh. Instead packages need to be loaded from the absolute root, regardless of whether a base is used or not.
• Fixes Astro 3.0 dev server error when base path is set and React component loaded #8352

Testing

• Tested in a demo project.
• Can't be tested in our integration tests due to it requiring the browser loading the module.

Docs

N/A, bug fix

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[bluwy]

LGTM. Seems like it's able to serve both with and without a basepath. The error was happening because we inject a script that's processed by Vite. Injecting as an inline script could also solve this.

[matthewp]

Astro's 'head-inline' scripts are non-module scripts so that wouldn't work here. Going with this as it seems to work.