VideoEncoder: Return unsupported for codec strings with spaces

This patch fixes a crash that occurs when a codec string with leading
spaces is passed to `VideoEncoder::IsConfigSupported`.

The crash happens because `VideoEncoderConfigInternal::ToEncoderConfig`
assumes that its codec string member begins with a supported codec name
(which should be non-space character). When the codec string has leading
spaces, this assumption is invalidated, leading to a crash.

To resolve this issue, the patch removes the space-trimming in
`CanEncode` and calling `IsSupportedVideoCodec` with the given codec
string directly before `ToEncoderConfig`. By doing so, codec strings
with leading spaces are correctly identified as "unsupported", and
`ToEncoderConfig` is not invoked with invalid input, preventing the
crash.

Additionally, this patch adds a WPT to ensure that codec string
containing spaces are reported as "unsupported" and the no crash occurs
when such strings are processed.

Differential Revision: https://phabricator.services.mozilla.com/D231719

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1936352
gecko-commit: 00a6b47b218e193d0018ffbd2996e0112d2a90f3
gecko-reviewers: media-playback-reviewers, alwu

webcodecs/video-encoder-config.https.any.js

@@ -183,6 +183,14 @@ const validButUnsupportedConfigs = [
       height: 480,
     },
   },
+  {
+    comment: 'codec with spaces',
+    config: {
+      codec: '  vp09.00.10.08  ',
+      width: 640,
+      height: 480,
+    }
+  }
 ];
 
 validButUnsupportedConfigs.forEach(entry => {