Zope.app.component

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- No longer using deprecated ``zope.testing.doctest``. Use python's build-in
``doctest`` instead.

- Replaced the dependency on ``zope.deferredimport`` with BBB imports.

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- Added missing BBB import in ``zope.app.component.metaconfigure``.

- Requiring at least ``zope.component`` 3.8 where some modules have
moved which are BBB imported here.

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- Import hooks functionality from zope.component after it was moved there from
zope.site.

- Import ISite and IPossibleSite from zope.component after they were moved
there from zope.location. This lifts the direct dependency on zope.location.

- Fix tests using a newer zope.publisher that requires zope.login.

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- Removed unnecessary dependency on ``zope.app.interface``.

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- Fix missing import in ``zope.app.component.metadirectives``.

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- Add deprecation note.