This widens the assertion from only checking if the WritableStream's
state is Errored or Erroring to asserting that the WritableStream is not
in a Writable state.
Our existing implementation of stream piping was extremely ad-hoc. It
did nothing to handle closed/errored streams, and did not read from or
write to streams in a way required by the spec.
This new implementation uses a custom JS::Cell to drive the read/write
loop.
This allows us to disable test output, which performs expensive assert
tracking. This was making our imported tests run significantly slower
than tests run via `WPT.sh`.
Formatting the output ourselves also allows us to remove unnecessary
information from the test output.
This commit also rebaselines all existing imported WPT tests to follow
the new format.
