moves all handling of the "contacts" root folder presence into
the contacts container cache. This ensures we can
remove any one-off code specifically targeting contacts'
peculiar root folder handling out of generic code paths and into
a data-specific owner.
The addition of a "defaultRootLocation" api is necessary otherwise
the cache lookup on restore always fails (or worse, gets confused
by the well known folder and an identically named subfolder),
and we end up with 409 responses and other issues.
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