Extract internal part as the function `str_chilled_p` #471

Job	Run time
ruby-versions / Generate Ruby versions	2s
ubuntu-24.04 2.7	41s
ubuntu-24.04 3.0	11s
ubuntu-24.04 3.1	19s
ubuntu-24.04 3.2	15s
ubuntu-24.04 3.3	12s
ubuntu-24.04 3.4	11s
ubuntu-24.04 debug	19s
ubuntu-24.04 head	12s
ubuntu-24.04 jruby-head	1m 14s
ubuntu-24.04 truffleruby-head	26s
ubuntu-22.04 2.7	40s
ubuntu-22.04 3.0	15s
ubuntu-22.04 3.1	18s
ubuntu-22.04 3.2	26s
ubuntu-22.04 3.3	15s
ubuntu-22.04 3.4	13s
ubuntu-22.04 debug	21s
ubuntu-22.04 head	13s
ubuntu-22.04 jruby-head	1m 7s
ubuntu-22.04 truffleruby-head	25s
	8m 15s

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