Add `GenerateAdapters` annotation #251

Job	Run time
check-score (hive)	1m 32s
code-quality (hive, stable)	1m 15s
ensure-codegen	3m 4s
code-quality (hive, beta)	5m 57s
ensure-embedme	8s
code-quality (hive_flutter, stable)	1m 22s
check-score (hive_flutter)	2m 0s
check-score (hive_generator)	2m 40s
code-quality (hive_flutter, beta)	1m 26s
test-hive (vm, kernel)	59s
code-quality (hive_generator, stable)	1m 17s
test-hive_flutter (stable)	50s
test-hive (chrome, dart2js)	4m 25s
code-quality (hive_generator, beta)	1m 11s
test-hive_generator (stable, ubuntu-latest)	1m 17s
test-hive_flutter (beta)	53s
test-hive (chrome, dart2wasm)	2m 47s
test-hive_generator (stable, windows-latest)	2m 43s
test-hive_generator (beta, ubuntu-latest)	1m 17s
	37m 3s

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