This got added in scoped-element 2.1.0 and is more or less the same
as getShadowRootDocument()

In case the scoped registry polyfill is loaded we need to create
elements inside of the shadowroot.

getShadowRootDocument() returns the polyfilled shadowroot, or in case
the polyfill is not loaded just return the global document, which works
in case there are no scoped registries.

In case we get something like https://github.com/open-wc/open-wc/pull/2389
this will be usefull. Also it makes IDE completion work + eslint.

This reverts commit 6c632dc6

This reverts commit 6324718b.

This reverts commit 3716524b.