Move outline drawing to Decoration::paint
Instead of drawing window outline in the shadow drawcall, draw it on top of border instead.
This helps keeping the outline size in sync with the window size and has less glitches.
Also moved shadow a tiny bit under the window, so it wont snap from next of the window when using fractional scaling.
Should at the very least alleviate the issues, if not fix them all.
(cherry picked from commit 6171b3fe)