Add clang format and editorconfig files. #4299

Job	Run time
arches	1s
mir-libs (amd64)	18m 39s
mir-libs (armhf)	1h 12m 51s
mir-libs (arm64)	34m 54s
snap (canonical/mir-test-tools, amd64)	13m 15s
snap (canonical/mir-test-tools, armhf)	27m 31s
snap (canonical/mir-test-tools, arm64)	58m 43s
snap (canonical/confined-shell-wip, amd64)	8m 26s
snap (canonical/confined-shell-wip, armhf)	24m 29s
snap (canonical/confined-shell-wip, arm64)	16m 39s
snap (canonical/ubuntu-frame, amd64)	3m 46s
snap (canonical/ubuntu-frame, armhf)	7m 45s
snap (canonical/ubuntu-frame, arm64)	10m 7s
snap (Miriway/Miriway, amd64)	8m 59s
snap (Miriway/Miriway, armhf)	17m 9s
snap (Miriway/Miriway, arm64)	25m 2s
	5h 48m 16s

Provide feedback