add link to detailed description of migration plan in deprecation message

Author: Guest0x0

builtin/iter.mbt

@@ -145,7 +145,7 @@ pub fn[T] Iter::count(self : Iter[T]) -> Int {
 
 ///|
 /// Do not use this method, it is for internal use only.
-#deprecated("`Iter::new`, and the internal iterator type `Iter`, is deprecated. Create an external iterator `Iterator`, and use `Iterator::iter` to migrate usage of `Iter::new`. `Iter` will become an alias of `Iterator` in the future.")
+#deprecated("`Iter::new`, and the internal iterator type `Iter`, is deprecated. Create an external iterator `Iterator`, and use `Iterator::iter` to migrate usage of `Iter::new`. `Iter` will become an alias of `Iterator` in the future. See https://github.com/moonbitlang/core/pull/3050 for more details.")
 pub fn[T] Iter::new(f : ((T) -> IterResult) -> IterResult) -> Iter[T] {
   Iter(f)
 }

builtin/iter2.mbt

@@ -55,7 +55,7 @@ pub impl[A : Show, B : Show] Show for Iter2[A, B] with output(self, logger) {
 }
 
 ///|
-#deprecated("`Iter2::new`, and the internal iterator type `Iter2`, is deprecated. Create an external iterator `Iterator2`, and use `Iterator2::iter2` to migrate usage of `Iter2::new`. `Iter2` will become an alias of `Iterator2` in the future.")
+#deprecated("`Iter2::new`, and the internal iterator type `Iter2`, is deprecated. Create an external iterator `Iterator2`, and use `Iterator2::iter2` to migrate usage of `Iter2::new`. `Iter2` will become an alias of `Iterator2` in the future. See https://github.com/moonbitlang/core/pull/3050 for more details.")
 pub fn[A, B] Iter2::new(
   f : ((A, B) -> IterResult) -> IterResult,
 ) -> Iter2[A, B] {