[move] fixed find_index (MystenLabs#18842)

## Description 

- Fixed find_index not being by-ref

## Test plan 

- new tests that force no `copy` possible

---

## Release notes

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crates/sui-framework/packages/move-stdlib/sources/vector.move

@@ -238,7 +238,7 @@ module std::vector {
 
     /// Finds the index of first element in the vector `v` that satisfies the predicate `f`.
     /// Returns `some(index)` if such an element is found, otherwise `none()`.
-    public macro fun find_index<$T>($v: vector<$T>, $f: |&$T| -> bool): Option<u64> {
+    public macro fun find_index<$T>($v: &vector<$T>, $f: |&$T| -> bool): Option<u64> {
         let v = $v;
         'find_index: {
             v.length().do!(|i| if ($f(&v[i])) return 'find_index option::some(i));

crates/sui-framework/packages/move-stdlib/tests/vector_tests.move

@@ -677,6 +677,11 @@ module std::vector_tests {
         let r = vector[0, 10, 100, 1_000];
         assert!(r.find_index!(|e| *e == 100).destroy_some() == 2);
         assert!(r.find_index!(|e| *e == 10_000).is_none());
+
+        let v = vector[Droppable{}, Droppable{}];
+        let idx = v.find_index!(|e| e == Droppable{});
+        assert!(idx.destroy_some() == 0);
+        assert!(&v[idx.destroy_some()] == Droppable{});
     }
 
     #[test]

external-crates/move/crates/move-analyzer/tests/dot_completion.exp

@@ -107,7 +107,7 @@ Method 'filter!()'
 Method 'find_index!()'
     INSERT TEXT: 'find_index!(|${1}| ${2})'
     TARGET     : '(std::vector::find_index)'
-    TYPE       : 'fun <$T>(vector<$T>, |&$T| -> bool): Option'
+    TYPE       : 'fun <$T>(&vector<$T>, |&$T| -> bool): Option'
 Method 'fold!()'
     INSERT TEXT: 'fold!(${1:init}, |${2}, ${3}| ${4})'
     TARGET     : '(std::vector::fold)'

external-crates/move/crates/move-stdlib/sources/vector.move

@@ -238,7 +238,7 @@ module std::vector {
 
     /// Finds the index of first element in the vector `v` that satisfies the predicate `f`.
     /// Returns `some(index)` if such an element is found, otherwise `none()`.
-    public macro fun find_index<$T>($v: vector<$T>, $f: |&$T| -> bool): Option<u64> {
+    public macro fun find_index<$T>($v: &vector<$T>, $f: |&$T| -> bool): Option<u64> {
         let v = $v;
         'find_index: {
             v.length().do!(|i| if ($f(&v[i])) return 'find_index option::some(i));

external-crates/move/crates/move-stdlib/tests/vector_tests.move

@@ -677,6 +677,11 @@ module std::vector_tests {
         let r = vector[0, 10, 100, 1_000];
         assert!(r.find_index!(|e| *e == 100).destroy_some() == 2);
         assert!(r.find_index!(|e| *e == 10_000).is_none());
+
+        let v = vector[Droppable{}, Droppable{}];
+        let idx = v.find_index!(|e| e == Droppable{});
+        assert!(idx.destroy_some() == 0);
+        assert!(&v[idx.destroy_some()] == Droppable{});
     }
 
     #[test]