Redo instance variables #2348

Job	Run time
Check MSRV	1m 10s
Check formatting	8s
Lint macOS 64bit	2m 38s
Lint iOS 32bit	58s
Lint GNUStep + exceptions	1m 28s
Lint header-translator	26s
Lint test-assembly	27s
Test macOS 12	7m 47s
Assembly tests	52s
Verify header translator output	59s
Check icrate features	0s
${{ matrix.name }}	0s
Test Compiler-RT	35s
Test GNUStep with libobjc2 v1.9	1m 39s
Test on iOS simulator w. dinghy	0s
Compiler UI	2m 1s
Test GNUStep with libobjc2 v2.0	1m 32s
Test GNUStep with libobjc2 v2.1 on nightly	2m 10s
Test GNUStep 32bit	52s
	25m 42s

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