Support #[method_family = ...] in `define_class!` #3377

Job	Run time
Lint macOS x86_64	3m 52s
Check MSRV	1m 4s
Lint iOS ARMv7s	4m 15s
Check formatting	12s
Lint visionOS Aarch64 simulator	4m 4s
Lint GNUStep + exceptions	1m 34s
Lint header-translator	36s
Lint test-assembly	25s
Test macOS 15 Aarch64	2m 14s
Assembly tests	54s
Verify header translator output	2m 55s
Check framework features	0s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test Compiler-RT	35s
Test GNUStep with libobjc2 v1.9	1m 24s
Test on iOS simulator w. dinghy	0s
Compiler UI	45s
Test GNUStep with libobjc2 v2.0	1m 26s
Test GNUStep with libobjc2 v2.1 on nightly	1m 3s
Test GNUStep 32bit	1m 20s
	28m 38s

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