AbortSignals not associated with a particular operation

[reillyeon]

As specified an AbortSignal passed as an option to scan(), write() or makeReadOnly() is not explicitly linked to that operation. This is theoretically fine because only one instance of those operations to exist at once but since we add the abort steps before performing such checks and the abort steps aren't specific about cancelling only the operation for which that signal was passed there is opportunity for an AbortSignal to abort an unrelated operation when it is signaled.

[reillyeon]

This came up in a Chromium change which adds support for removing abort algorithms, highlighting that this specification doesn't actually cover this case consistently.