Add speech recognition and synthesis features (web-platform-dx#506)

Co-authored-by: Daniel D. Beck <[email protected]>

Author: foolip

feature-group-definitions/speech-recognition.yml

@@ -0,0 +1,4 @@
+name: Speech recognition
+spec: https://wicg.github.io/speech-api/#speechreco-section
+caniuse: speech-recognition
+usage_stats: https://chromestatus.com/metrics/feature/timeline/popularity/2014

feature-group-definitions/speech-synthesis.yml

@@ -0,0 +1,4 @@
+name: Speech synthesis
+spec: https://wicg.github.io/speech-api/#tts-section
+caniuse: speech-synthesis
+usage_stats: https://chromestatus.com/metrics/feature/timeline/popularity/2483