Expose shouldSmoothscroll() as part of public API

[jonaskuske]

Giving users access to smoothscrollAnchorPolyfill.shouldSmoothscroll() would allow userland implementations for JS scroll APIs to stay in sync with the behavior detected by this polyfill.

Something along the lines of:

const scroll = scrollTo = function (opts = {}) {
  if (!opts.behavior && shouldSmoothscroll()) {
    opts.behavior = 'smooth'
  }
  const container = this instanceof Element ? this : window
  container.scroll(opts)
}

Renaming the API should be considered too, as well as maybe returning the detected behavior as a string (smooth|auto|initial|inherit|unset) instead of a simple boolean.