refactor(core): CORE-01 migrate utility contracts to TypeScript

packages/artplayer/src/utils/file.ts

@@ -0,0 +1,19 @@
+export function getExt(url: string): string {
+  const end = url.search(/[?#]/)
+  const clean = (end < 0 ? url : url.slice(0, end)).trim().toLowerCase()
+  return clean.slice(clean.lastIndexOf('.') + 1)
+}
+
+export function download(url: string, name: string): void {
+  const elink = document.createElement('a')
+  elink.style.display = 'none'
+  elink.href = url
+  elink.download = name
+  document.body.appendChild(elink)
+  try {
+    elink.click()
+  }
+  finally {
+    elink.remove()
+  }
+}