Update interfaces/media-capabilities.idl (#19906)

Source: https://github.com/tidoust/reffy-reports/blob/9974098/ed/idl/media-capabilities.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/603089848
diff --git a/interfaces/media-capabilities.idl b/interfaces/media-capabilities.idl
index e067fdc..71bc46d 100644
--- a/interfaces/media-capabilities.idl
+++ b/interfaces/media-capabilities.idl
@@ -84,6 +84,11 @@
 
 dictionary MediaCapabilitiesDecodingInfo : MediaCapabilitiesInfo {
   required MediaKeySystemAccess keySystemAccess;
+  MediaDecodingConfiguration configuration;
+};
+
+dictionary MediaCapabilitiesEncodingInfo : MediaCapabilitiesInfo {
+  MediaEncodingConfiguration configuration;
 };
 
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