Update optical_size.textproto (#2989)

Add 17pt

axisregistry/optical_size.textproto

@@ -43,6 +43,10 @@ fallback {
   name: "16pt"
   value: 16
 }
+fallback {
+  name: "17pt"
+  value: 17
+}
 fallback {
   name: "18pt"
   value: 18