Rewrite <LoadingIndicator/> as FC and TS (#25364)

app/javascript/mastodon/components/circular_progress.tsx

@@ -0,0 +1,27 @@
+interface Props {
+  size: number;
+  strokeWidth: number;
+}
+
+export const CircularProgress: React.FC<Props> = ({ size, strokeWidth }) => {
+  const viewBox = `0 0 ${size} ${size}`;
+  const radius = (size - strokeWidth) / 2;
+
+  return (
+    <svg
+      width={size}
+      height={size}
+      viewBox={viewBox}
+      className='circular-progress'
+      role='progressbar'
+    >
+      <circle
+        fill='none'
+        cx={size / 2}
+        cy={size / 2}
+        r={radius}
+        strokeWidth={`${strokeWidth}px`}
+      />
+    </svg>
+  );
+};