Refactor: re-throw error on load

[katspaugh]

Short description

A follow-up on #3532.

Implementation details

• The error event handler now takes an Error object
• Async fetching/decoding errors in the constructor are now caught and emitted as an error event.
• Calling load and loadBlob will still result in a rejected promise on error (it was swallowed in the original PR), while also emitting an error event.
• Remove a breaking blob check.

[github-actions]

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	1	N/A

• Result: ✅ success
• Annotations: 0 total

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