Make SIP-62 `better-fors` a stable feature #170

Job	Run time
scala-library-nonbootstrapped	1m 0s
tasty-core-bootstrapped	4m 8s
scala3-compiler-nonbootstrapped	3m 23s
tasty-core-nonbootstrapped	58s
scala3-library-bootstrapped	4m 3s
scala3-library-nonbootstrapped	1m 0s
scala3-staging	5m 31s
scala3-sbt-bridge-nonbootstrapped	3m 44s
test-scala3-sbt-bridge-nonbootstrapped	3m 27s
scala3-sbt-bridge-bootstrapped	5m 57s
test-tasty-core-bootstrapped	4m 16s
test-tasty-core-nonbootstrapped	1m 5s
scala3-tasty-inspector	6m 8s
scala3-compiler-bootstrapped	5m 53s
test-scala3-sbt-bridge-bootstrapped	5m 53s
scala-library-bootstrapped	4m 13s
	1h 0m 39s

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