Add bridgeCommand helper function

ts/graphs/GraphsPage.svelte

@@ -8,6 +8,7 @@
     import type pb from "anki/backend_proto";
     import { getGraphData, RevlogRange, daysToRevlogRange } from "./graph-helpers";
     import { getPreferences } from "./preferences";
+    import { bridgeCommand } from "anki/bridgecommand";
 
     export let i18n: I18n;
     export let nightMode: boolean;

ts/lib/bridgecommand.ts

@@ -1,7 +1,17 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
+declare global {
+    interface Window {
+        bridgeCommand<T>(command: string, callback?: (value: T) => void): void;
+    }
+}
+
 /// HTML <a> tag pointing to a bridge command.
 export function bridgeLink(command: string, label: string): string {
     return `<a href="javascript:bridgeCommand('${command}')">${label}</a>`;
 }
+
+export function bridgeCommand<T>(command: string, callback?: (value: T) => void): void {
+    window.bridgeCommand<T>(command, callback);
+}