This change updates legacy type hints that use the old Optional[...] form

to be (... | None) instead. This change covers the extensions,

hostingsvcs, licensing, notifications, search, site,

testing, and themes subdirs.
Because I want to keep this tightly focused and easy to review, this

does not make any changes to other legacy type hints, documentation,

etc., even within the changed lines. Those will come in future changes.

Ran unit tests.