[WebCodecs] schedule dequeue event when encoder queue size decreases

https://bugs.webkit.org/show_bug.cgi?id=247000
rdar://problem/101539115

Reviewed by Eric Carlson.

Schedule event as per spec.

* LayoutTests/imported/w3c/web-platform-tests/webcodecs/video-encoder.https.any-expected.txt:
* Source/WebCore/Modules/webcodecs/WebCodecsVideoEncoder.cpp:
(WebCore::WebCodecsVideoEncoder::encode):

Canonical link: https://commits.webkit.org/255962@main

LayoutTests/imported/w3c/web-platform-tests/webcodecs/video-encoder.https.any-expected.txt

@@ -2,7 +2,7 @@
 PASS Test VideoEncoder construction
 PASS Test VideoEncoder.configure()
 FAIL Test successful configure(), encode(), and flush() promise_test: Unhandled rejection with value: object "TypeError: undefined is not an object (evaluating 'decoderConfig.colorSpace.primaries')"
-FAIL encodeQueueSize test assert_equals: expected 0 but got Infinity
+PASS encodeQueueSize test
 PASS Test successful reset() and re-confiugre()
 PASS Test successful encode() after re-configure().
 PASS Verify closed VideoEncoder operations

Source/WebCore/Modules/webcodecs/WebCodecsVideoEncoder.cpp

@@ -210,6 +210,7 @@ ExceptionOr<void> WebCodecsVideoEncoder::encode(Ref<WebCodecsVideoFrame>&& frame
     ++m_encodeQueueSize;
     queueControlMessageAndProcess([this, internalFrame = internalFrame.releaseNonNull(), timestamp = frame->timestamp(), duration = frame->duration(), options = WTFMove(options)]() mutable {
         --m_encodeQueueSize;
+        scheduleDequeueEvent();
         m_internalEncoder->encode({ WTFMove(internalFrame), timestamp, duration }, options.keyFrame, [this, weakedThis = WeakPtr { *this }](auto&& result) {
             if (!weakedThis)
                 return;