WritableStream: [[error]] must replace writablePromise when in readable state

When a WritableStream is in readable state, writablePromise is set to a
fulfilled promise. We need to replace it with a new rejected promise.

In writable-stream-abort.js, 'Aborting a WritableStream causes ...' test is
testing a WritableStream in writable state which now returns a pending
promise which gets rejected but this should be a fulfilled promise to be
consistent with the initial value of [[state]] that is 'writable'. We need
to fix this behavior later but for now just put the WritableStream in
'waiting' state and test what stated in the test description.