Add C API rb_enc_interned_str_cstr function #4414

Job	Run time
build jvm	7m 4s
build native	14m 4s
ruby/spec on CRuby 3.0	3m 25s
lint	12m 51s
ruby/spec on CRuby 3.1	3m 22s
ruby/spec on CRuby 3.2	2m 48s
fast specs	1m 52s
test integration	9m 2s
specs :truffle	8m 58s
specs :language :core	11m 4s
specs :library :cext :security :command_line :tracepoint	8m 42s
run MRI tests on native	13m 51s
test native	3m 5s
	1h 40m 8s

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