Add separate interface library KDev::IExecute for execute/iexecuteplugin.h
Summary:
Avoids adding the ${KDevPlatform_SOURCE_DIR}/plugins dir to the
include dirs of everything linking the "normal" libs
Reviewers: KDevelop, kfunk
Reviewed By: KDevelop, kfunk
Subscribers: kfunk, kdevelop-devel
Differential Revision: https://phabricator.kde.org/D7219