add missing externs to repo

externs/webextension_polyfill/identity/AccountInfo.hx

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+package webextension_polyfill.identity;
+
+/**
+	An object encapsulating an OAuth account id.
+**/
+typedef AccountInfo = {
+	/**
+		A unique identifier for the account. This ID will not change for the lifetime of the account.
+	**/
+	var id : String;
+};

externs/webextension_polyfill/identity/LaunchWebAuthFlowDetailsType.hx

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+package webextension_polyfill.identity;
+
+typedef LaunchWebAuthFlowDetailsType = {
+	var url : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var interactive : Bool;
+};

externs/webextension_polyfill/identity/Static.hx

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+package webextension_polyfill.identity;
+
+typedef Static = {
+	/**
+		Starts an auth flow at the specified URL.
+	**/
+	function launchWebAuthFlow(details:LaunchWebAuthFlowDetailsType):js.lib.Promise<String>;
+	/**
+		Generates a redirect URL to be used in |launchWebAuthFlow|.
+	**/
+	function getRedirectURL(?path:String):String;
+};