refactor: Replace Rollup with Vite (#2656)

This is a high risk change: every byte the card ships is emitted by a
different bundler, minified by a different minifier, and every
stylesheet is compiled by a different sass. The intent is that the
card's behaviour is unchanged.

**Significant development win**: Build time drops from 24s to 1.1s 🎉 

Also adds a test suite ('dist') that runs against the built bundle.

tests/dist/test-utils.ts

@@ -0,0 +1,30 @@
+/**
+ * Loads the module at `url` the same way Home Assistant puts a dashboard
+ * resource into one: by appending a script element for it. Resolves once the
+ * browser has fetched and run it.
+ *
+ * Rejects only when the file could not be fetched or parsed. A module that
+ * throws while running has still loaded, and reports itself to `window`
+ * instead.
+ */
+export const loadModule = async (url: string): Promise<void> =>
+  await new Promise((resolve, reject) => {
+    const script = document.createElement('script');
+    script.type = 'module';
+    script.async = true;
+    script.onload = () => resolve();
+    script.onerror = () => reject(new Error(`Could not load ${url}`));
+    script.src = url;
+
+    document.body.appendChild(script);
+  });
+
+/**
+ * Waits for the browser to get through the work it already has queued.
+ *
+ * Draining promises (as `flushPromises` does) reaches none of that work. An
+ * uncaught exception or a rejected promise nothing handled, for instance, is
+ * reported only once the browser has run out of work to do.
+ */
+export const flushBrowserWork = async (): Promise<void> =>
+  await new Promise((resolve) => setTimeout(resolve));