Expose the rb_interned_str_* family of functions

Fixes [Feature ruby#13381]

Author: byroot

include/ruby/encoding.h

@@ -127,6 +127,8 @@ void rb_enc_copy(VALUE dst, VALUE src);
 VALUE rb_enc_str_new(const char*, long, rb_encoding*);
 VALUE rb_enc_str_new_cstr(const char*, rb_encoding*);
 VALUE rb_enc_str_new_static(const char*, long, rb_encoding*);
+VALUE rb_enc_interned_str(const char *, long, rb_encoding *);
+VALUE rb_enc_interned_str_cstr(const char *, rb_encoding *);
 VALUE rb_enc_reg_new(const char*, long, rb_encoding*, int);
 PRINTF_ARGS(VALUE rb_enc_sprintf(rb_encoding *, const char*, ...), 2, 3);
 VALUE rb_enc_vsprintf(rb_encoding *, const char*, va_list);

include/ruby/internal/intern/string.h

@@ -74,6 +74,9 @@ VALUE rb_utf8_str_new_cstr(const char*);
 VALUE rb_str_new_static(const char *ptr, long len);
 VALUE rb_usascii_str_new_static(const char *ptr, long len);
 VALUE rb_utf8_str_new_static(const char *ptr, long len);
+VALUE rb_str_to_interned_str(VALUE);
+VALUE rb_interned_str(const char *, long);
+VALUE rb_interned_str_cstr(const char *);
 void rb_str_free(VALUE);
 void rb_str_shared_replace(VALUE, VALUE);
 VALUE rb_str_buf_append(VALUE, VALUE);

string.c

@@ -11402,6 +11402,36 @@ sym_all_symbols(VALUE _)
     return rb_sym_all_symbols();
 }
 
+VALUE
+rb_str_to_interned_str(VALUE str)
+{
+    return rb_fstring(str);
+}
+
+VALUE
+rb_interned_str(const char *ptr, long len)
+{
+    return rb_fstring_new(ptr, len);
+}
+
+VALUE
+rb_interned_str_cstr(const char *ptr)
+{
+    return rb_fstring_cstr(ptr);
+}
+
+VALUE
+rb_enc_interned_str(const char *ptr, long len, rb_encoding *enc)
+{
+    return rb_fstring_enc_new(ptr, len, enc);
+}
+
+VALUE
+rb_enc_interned_str_cstr(const char *ptr, rb_encoding *enc)
+{
+    return rb_fstring_enc_new(ptr, strlen(ptr), enc);
+}
+
 /*
  *  A String object holds and manipulates an arbitrary sequence of
  *  bytes, typically representing characters. String objects may be created