cherry-pick focus frames to Plasma 5.23
We got another bug report about focus visuals being lacking. The focus frame patch narrowly missed the window of time for Plasma 5.23, but it works pretty well and we haven't found any bugs related to it since it was merged ~3 weeks ago. We'll have until November 9th to find bugs in 5.23.3 if we cherry-pick this now. Perhaps we should include it in Plasma 5.23.3?
CCBUG: 443469 CCBUG: 444625
(cherry picked from commit 586e7462)