greeter: Fix Shader Wallpaper plugin and possibly others
Cherry-pick MR for !218 (merged). I was hoping that !226 (merged) gets merged first to see what the CI pipeline is all about, but better cherry-pick now before I forget about it.
Some wallpaper plugins make use of the "wallpaper" context property in bindings and on component completion. Assigning it only after the SharedQmlEngine finished loading is too late and can result in numerous QML reference errors.
Move assignment of the new SharedQmlEngine's context property further up to be called before component completion, and also set context properties for the containing view as all the necessary objects exist at that point.
(cherry picked from commit 29e085e7)
Co-authored-by: Jakob Petsovits jpetso@petsovits.com