fix: replace server.origin in css plugin (fix #5408)

[dbohn]

Description

Pull Request #5104 introduced the server.origin configuration option to set a base URL for static assets.
This was implemented by checking for this option in the fileToDevUrl function of the assets plugin.
This function is used by the css plugin as well when registering CSS files as build dependencies.
This lead to incorrect added watch dependencies and broke HMR for Tailwind as described in #5408

This PR fixes this issue by adding the server origin to the already present replace call, that removed the config.base, if the server.origin option is set and should fix #5408.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[Niputi]

would be good if you are able to add a test so there won't be regression

[dbohn]

I've updated the existing tailwind playground to include the server origin clause.
When doing so, the tests for this playground fail to run without the fix, but with the fix they pass.
As far as I can see, this is the best place to test for this as this is already pretty much the smallest reproduction, but if you think, there is a better way to test this, I would be happy to add this!