Add basic CFError Display and Error impls #3308

Job	Run time
Check formatting	10s
Check MSRV	1m 0s
Lint macOS x86_64	3m 25s
Lint iOS ARMv7s	3m 24s
Lint visionOS Aarch64 simulator	3m 11s
Lint GNUStep + exceptions	1m 24s
Lint header-translator	30s
Lint test-assembly	24s
Test macOS 15 Aarch64	1m 24s
Compiler UI	45s
Assembly tests	50s
Verify header translator output	2m 20s
Check framework features	0s
Test Compiler-RT	27s
${{ ((matrix.test && 'Test') \|\| 'Build') }} ${{ matrix.name }}	0s
Test GNUStep with libobjc2 v1.9	1m 1s
Test on iOS simulator w. dinghy	0s
Test GNUStep with libobjc2 v2.0	1m 9s
Test GNUStep with libobjc2 v2.1 on nightly	56s
Test GNUStep 32bit	1m 7s
	23m 27s

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