fix(ssr): make import.meta.url be the filesystem URL

[matthewp]

Description

This makes import.meta.url be the file URL, the same as in Node ESM, Deno, Webpack, etc.

Additional context

This is a spinoff from #5252

---

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.

[patak-dev]

See #5252 (comment) for reference, from @matthewp:

I deployed a test project in Cloudflare and import.meta.url is undefined. If you use their webpack template then it's the local filesystem URL as expected (because webpack is building to commonjs).

If it is undefined, it may be that they haven't yet implemented support in webworkers. We should keep an eye on this, as we may need to update the handling depending on ssr.target later.