Move ECM & Co. macro includes before finding Qt & KF

Summary:
For consistency with other Plasma repos, but also to ensure the ECM
logic for supporting uninstalled unit tests is properly triggered
See
https://api.kde.org/ecm/kde-module/KDECMakeSettings.html#build-settings

Including KDECMakeSettings only after finding KF5CoreAddons and the
implicit loading of KF5PlasmaMacros/KF5PackageMacros resets the
ECM_GLOBAL_FIND_VERSION variable to the min ECM value 1.6.0 currently
used by those macro files, thus below the trigger value 5.38

Test Plan: Still builds and installs as before.

Reviewers: gladhorn, sebas, romangg, apol

Reviewed By: apol

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D14031