feat: File Upload Progress

[ottomated]

see #14773

Builds on #14775 to use XHRs for file upload progress in forms:

<script>
  import { uploadForm } from './upload.remote';
</script>

<form {...uploadForm} enctype="multipart/form-data">
  <input {...uploadForm.fields.file.as('file')} />
  <p>Progress: {(uploadForm.fields.file.progress().uploaded / (uploadForm.fields.file.progress().total).toFixed(2)}%</p>
  <button>Upload</button>
</form>

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🦋 Changeset detected

Latest commit: eee49935f805048555e9c7e454298106d948ea15

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

This PR includes changesets to release 1 package

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@sveltejs/kit	Minor

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[ottomated]

paging @Rich-Harris to see if this can go out with #14775 :-)