Rollup merge of #106950 - the8472:fix-splice-miri, r=cuviper

Don't do pointer arithmetic on pointers to deallocated memory

vec::Splice can invalidate the slice::Iter inside vec::Drain. So we replace them with dangling pointers which, unlike ones to deallocated memory, are allowed.

Fixes miri test failures.
Fixes #2759

Author: Dylan-DPC

tests/pass/vec.rs

@@ -162,6 +162,11 @@ fn reverse() {
     assert!(v[0].0 == 49);
 }
 
+fn miri_issue_2759() {
+    let mut input = "1".to_string();
+    input.replace_range(0..0, "0");
+}
+
 fn main() {
     assert_eq!(vec_reallocate().len(), 5);
 
@@ -191,4 +196,5 @@ fn main() {
     swap();
     swap_remove();
     reverse();
+    miri_issue_2759();
 }