chore(common): remove url module ref from common/web/types

The url module is a node module. We need to move responsibility for
resolving the path of the LDML XML <import> statements out of
common/web/types, and into the ultimate consumer, so it's now surfaced
as an option, along with a helper constant that reports the
import.meta.url-relative base path of the standard imports that are
compiled into common/web/types.

This hopefully means we can use this module in both browser and node
contexts without trouble.