When a promise is aborted using AbortSignal, the reason of the abort is not preserved

[logan-gatlin]

When a promise is aborted using AbortSignal, the reason of the abort is not preserved - it becomes a generic error object instead. This caused a number of new WPT test failures (#7021):

• Aborting rejects with abort reason when aborted after fetch() called
• response.arrayBuffer() rejects with abort reason if already aborted
• response.blob() rejects with abort reason if already aborted
• response.bytes() rejects with abort reason if already aborted
• response.formData() rejects with abort reason if already aborted
• response.json() rejects with abort reason if already aborted
• response.text() rejects with abort reason if already aborted
• Stream errors once aborted with abort reason. Underlying connection closed.

There are also several tests that predate #7021 and are marked as expected failures, for the same reasons:

• Aborting rejects with AbortError
• Aborting rejects with abort reason
• Already aborted signal rejects immediately

This is probably due to exception tunneling.