fix: update extern type syntax

Author: peter-jerry-ye

legacy/examples/snake/extern/string.wasm.mbt

@@ -12,13 +12,13 @@
 //  See the License for the specific language governing permissions and
 //  limitations under the License.
 
-priv type JsArray
+priv extern type JsArray
 
 fn JsArray::new() -> JsArray = "array" "new"
 
 fn push(self : JsArray, charCode : Int) = "array" "push"
 
-pub(all) type JsString
+pub(all) extern type JsString
 
 fn JsString::from_char_code(charCode : JsArray) -> JsString = "string" "fromCharCode"
 

legacy/examples/snake/lib/draw.mbt

@@ -12,7 +12,7 @@
 //  See the License for the specific language governing permissions and
 //  limitations under the License.
 
-pub(all) type Canvas_ctx
+pub(all) extern type Canvas_ctx
 
 fn body_color(grid : GridType) -> String {
   match grid {

next/language/error_codes/E4042.md

@@ -26,7 +26,7 @@ you can pass the int one by one to the host function and store the array on the
 JS side.
 
 ```moonbit
-type JsArray
+extern type JsArray
 fn make_js_array() -> JsArray = "mod" "make_js_array"
 fn push_js_array(array : JsArray, value : Int) -> Unit = "mod" "push_js_array"
 ```