The encoder/decoder configure methods is not using a queue to check for configuration support

[youennf]

Following on https://github.com/web-platform-tests/interop/issues/382#issuecomment-1731669384 and https://github.com/web-platform-tests/wpt/pull/42127, we could improve the spec related to the configure methods.

In particular:

• configure should probably be using a parallel queue to check for configuration support, like isConfigSupported is.
• once the check is done and config is not supported, configure could queue a task to call the close decoder/encoder algorithm, like done in https://w3c.github.io/webcodecs/#dom-audiodecoder-decode. This would work nicely if we change the close decoder algorithm to synchronously call the error callback.

Other editorial notes while reading the spec (probably applicable to all decoders/encoders) :

• isConfigSupported is trying to resolve a promise from a parallel queue, we could instead queue a task to resolve the promise.
• [[message queue blocked]] is accessed from both the work queue and the event task queue, for instance in https://w3c.github.io/webcodecs/#dom-audiodecoder-configure. It might be better to queue a task to set [[message queue blocked]] to false and synchronously process the control queue.
• Ditto for [[codec saturated]] which seems to be accessed from both the codec work queue and the event task queue.

[youennf]

@dalecurtis, I filed this issue following on our WPT test discussions. Let me know if that aligns with your thoughts. I can also submit the corresponding PR(s) if that helps.

[dalecurtis]

I'm not sure about [[codec saturated]] since that might have performance implications, but the rest sgtm and matches what our implementation (after the recent fixes). Your help with the PRs would be most welcome, thanks!

[youennf]

Additional remark related to [[codec implementation]]as spec says it should only be used from the [[codec queue]]. But the spec currently signals or clears [[codec implementation]] from reset/close algorithms, which can be called from JS directly, without queueing a task to the [[codec queue]].