ContextAwarePluginBase::setContextValue() should delegate to ::setContext()

Problem/Motivation

ContextAwarePluginBase provides the method setContext() as its primary setter.
It also provides setContextValue() as a convenience method.

However, setContextValue() currently bypasses setContext(), so any class that wants to override one setter must override the other.

Proposed resolution

Make setContextValue() use setContext() internally

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A