Force ensure_valid_encoding to be inlined.

And move the encoding convertion logic in another function with NOINLINE.

The overwelming majority of strings are correctly encoded, so we
want to inline the very cheap check, however we don't want to
inline the much larger piece of code required to re-encode the string.

Co-Authored-By: Jean Boussier <jean.boussier@gmail.com>

Author: samyron

ext/json/ext/generator/generator.c

@@ -842,12 +842,8 @@ static inline bool valid_json_string_p(VALUE str)
     return false;
 }
 
-static inline VALUE ensure_valid_encoding(struct generate_json_data *data, VALUE str, bool as_json_called, bool is_key)
+NOINLINE(static) VALUE convert_invalid_encoding(struct generate_json_data *data, VALUE str, bool as_json_called, bool is_key)
 {
-    if (RB_LIKELY(valid_json_string_p(str))) {
-        return str;
-    }
-
     if (!as_json_called && data->state->strict && RTEST(data->state->as_json)) {
         VALUE coerced_str = json_call_as_json(data->state, str, Qfalse);
         if (coerced_str != str) {
@@ -883,6 +879,16 @@ static inline VALUE ensure_valid_encoding(struct generate_json_data *data, VALUE
     return rb_rescue(encode_json_string_try, str, encode_json_string_rescue, str);
 }
 
+ALWAYS_INLINE(static) VALUE ensure_valid_encoding(struct generate_json_data *data, VALUE str, bool as_json_called, bool is_key)
+{
+    if (RB_LIKELY(valid_json_string_p(str))) {
+        return str;
+    }
+    else {
+        return convert_invalid_encoding(data, str, as_json_called, is_key);
+    }
+}
+
 static void raw_generate_json_string(FBuffer *buffer, struct generate_json_data *data, VALUE obj)
 {
     fbuffer_append_char(buffer, '"');