Export injectStyles so the polyfill can work with Lit

[Totati]

Hi, we
This polyfill does not work well with Lit, as Lit overrides the adoptedStyleSheets in the first connectedCallback.

Currently I could overcome this by overriding the Lit's ReactiveElement#createRenderRoot with a custom implementation, so it spreads the current adopted styles, but it's not a patch.

When injectStyles is exported it can be patched with way less code, keeping the original implementation.

  const originalCreateRenderRoot = (ReactiveElement as any).prototype.createRenderRoot;
  (ReactiveElement as any).prototype.createRenderRoot = function () {
    const renderRoot = originalCreateRenderRoot.call(this);
    injectStyles(renderRoot);
    return renderRoot;
  };

[jgerigmeyer]

@Totati Thanks for reporting! This is released in v0.4.3.