This commit picks up where SPR-14614 left off by introducing a new
@EnabledIf annotation to serve as a logical companion to @DisabledIf.
In addition, this commit extracts common logic from DisabledIfCondition
into a new AbstractExpressionEvaluatingCondition base class which the
new EnabledIfCondition also extends.
An @EnabledOnMac annotation is also included in the Javadoc as well as
in the test suite to demonstrate support for custom composed annotations.
Issue: SPR-14644
634d1c03a3