Update the RegExp flag from "u" to "v"

[sisidovski]

In whatwg/urlpattern#188, the URL Pattern API was updated to use v flag instead of u. As mentioned in the blink-dev thread, the expected impact is very limited.

It would be great if the polyfill library follows, too. I can work on making a PR for this update.

[SanderElias]

@sisidovski Once the spec has merged this and the updated tests are available, we will update.
There is little value to update before unicode tests are added upstream.

[sisidovski]

@SanderElias Actually the spec was already merged. chromium is going to update the flag, too fyi (blink-dev thread). Here is the updated tests. web-platform-tests/wpt#43014