Add 'startScanning' method to expose externally

[Jkssns]

When I obtained the result by scanning the QR code, I presented it on the page and then deleted the result from the page, attempting to scan the same QR code again, but I was unable to obtain the result again.

I have tried the 'init' method, but the dom will be recreated, which is not ideal.

What I am currently doing is to stop scanning after deleting the results (ref. value. stopScanning), and in nextTick (ref. value. startScanning), I can obtain my results.