Redo instance variables #2359

Job	Run time
Check formatting	8s
Check MSRV	1m 12s
Lint macOS 64bit	2m 45s
Lint iOS 32bit	1m 9s
Lint GNUStep + exceptions	1m 31s
Lint header-translator	37s
Lint test-assembly	33s
Test macOS 12	9m 10s
Compiler UI	1m 49s
Verify header translator output	1m 20s
Assembly tests	1m 4s
Check icrate features	0s
Test Compiler-RT	23s
Test GNUStep with libobjc2 v1.9	1m 22s
Test GNUStep with libobjc2 v2.0	1m 31s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.1 on nightly	1m 58s
Test GNUStep 32bit	1m 45s
${{ matrix.name }}	0s
	28m 17s

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