Update comments to make it explicit that moving a flat_hash_{set,map} can cause…

Update comments to make it explicit that moving a flat_hash_{set,map} can cause pointers to elements to be invalidated.

PiperOrigin-RevId: 578920671
Change-Id: Ica40db48d5565b606e5e5f501c1305612b193d4d

absl/container/flat_hash_map.h

@@ -64,7 +64,7 @@ struct FlatHashMapPolicy;
 //   `insert()`, provided that the map is provided a compatible heterogeneous
 //   hashing function and equality operator.
 // * Invalidates any references and pointers to elements within the table after
-//   `rehash()`.
+//   `rehash()` and when the table is moved.
 // * Contains a `capacity()` member function indicating the number of element
 //   slots (open, deleted, and empty) within the hash map.
 // * Returns `void` from the `erase(iterator)` overload.

absl/container/flat_hash_set.h

@@ -60,7 +60,7 @@ struct FlatHashSetPolicy;
 //   that the set is provided a compatible heterogeneous hashing function and
 //   equality operator.
 // * Invalidates any references and pointers to elements within the table after
-//   `rehash()`.
+//   `rehash()` and when the table is moved.
 // * Contains a `capacity()` member function indicating the number of element
 //   slots (open, deleted, and empty) within the hash set.
 // * Returns `void` from the `erase(iterator)` overload.