add missing externs to repo

externs/webextension_polyfill/find/RectData.hx

@@ -0,0 +1,14 @@
+package webextension_polyfill.find;
+
+typedef RectData = {
+	/**
+		The index of the frame containing the match. 0 corresponds to the parent window. Note that the order of objects in the
+		rangeData array will sequentially line up with the order of frame indexes: for example,
+		framePos for the first sequence of rangeData objects will be 0, framePos for the next sequence will be 1, and so on.
+	**/
+	var rectsAndTexts : RectsAndTexts;
+	/**
+		The complete text of the match.
+	**/
+	var text : String;
+};