Just use onfocusin as a detection test for focusin support

Due to various restrictions on what dojo/on can depend on,
and a desire to resolve this issue so that a release can be issued,
simply check for a matching event key on the has-test element.
This stops focusin/focusout from being used in WebKit and Blink
in lieu of event capturing, which is not ideal, but is not any
worse than what was happening before.

Refs #17599.
Add missing host-node and host-rhino rules to has.js

Fixes #17741.
Use has.add for config-useDeferredInstrumentation

This ensures that a default build works the same as an unbuilt
version of Dojo, while still allowing the configuration value
to be fixed during a build.

Fixes #17753.