Add C API rb_enc_interned_str_cstr function #4395

Job	Run time
lint	13m 10s
build native	13m 43s
build jvm	6m 32s
ruby/spec on CRuby 3.0	3m 22s
ruby/spec on CRuby 3.1	3m 45s
ruby/spec on CRuby 3.2	2m 52s
specs :truffle	8m 49s
test integration	9m 3s
fast specs	1m 58s
specs :language :core	10m 59s
specs :library :cext :security :command_line :tracepoint	8m 41s
run MRI tests on native	14m 11s
test native	3m 5s
	1h 40m 10s

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