Fix url concatenation for dev mode with origin set in server options

[dknibbe]

• Quick Checklist

• I have read the contributing guidelines
• I have written new tests, as applicable (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• I have added a changeset, if applicable

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  This change contains a bug fix for the feature introduced in pull request Add vite origin support for image urls in development #690. The server origin option usually contains a protocol scheme identifier followed by a double slash, e.g. "http://localhost:1234". Nodes POSIX path implementation is not meant to join URLs, which means the double slash is converted to a single slash, resulting in an invalid URL, e.g "http:/localhost:1234". Using url-join instead ensures the result will be a valid URL.

• Other information:
  Added new dependency: url-join, which seams to be the safest option

[changeset-bot]

🦋 Changeset detected

Latest commit: ead219f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
vite-imagetools	Patch

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[benmccann]

I don't think we need to add a dependency for such a simple piece of functionality. Can you just add a method here to do it instead?

[dknibbe]

I changed it to string concatenation. This should work fine, because Vite makes sure that the origin option never ends with a '/'.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.69%. Comparing base (31c14f2) to head (ead219f).
Report is 4 commits behind head on main.

Files	Patch %	Lines
packages/vite/src/index.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #732      +/-   ##
==========================================
- Coverage   95.69%   95.69%   -0.01%     
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  Files          33       33              
  Lines        1278     1277       -1     
  Branches      224      224              
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- Hits         1223     1222       -1     
  Misses         55       55              

Flag	Coverage Δ
imagetools-core	95.69% <0.00%> (-0.01%)	⬇️
vite-imagetools	95.69% <0.00%> (-0.01%)	⬇️

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