Reject browser js loader promise with Error object

[mrkldshv]

↪️ Pull Request

If loading of JS in the browser fails, reject promise of JS loader with Error object with message instead of DOM Error event.
Fixes #6052.

🚨 Test instructions

Fake JS loader fail to get rejected promise and checked printed out error.

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

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[mischnic]

Ci is failing because you need to reformat the file with Prettier.

[mrkldshv]

@mischnic Formatting should be fixed now

[mrkldshv]

Thank you for review!