Copy .clang-format file from kwin
Currently, when editing outputdevice_v2_interface.{cpp,h}, clang-format is very unhappy about pre-existing code. There are also other places where code is formatted not properly. We need to run clang-format again, however while on this, let's copy kwin's clang-format file so style is consistent between two repos.
Edited by Vlad Zahorodnii