Add tests for issues rust-lang#763 and rust-lang#702 (rust-lang#812)

Author: danielsn

tests/kani/Vectors/fixme_702.rs

@@ -0,0 +1,18 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// Failing example from https://github.com/model-checking/kani/issues/702
+// Push 5 elements to force the vector to resize, then check that the values were correctly copied.
+fn main() {
+    let mut v = Vec::new();
+    v.push(72);
+    v.push(2);
+    v.push(3);
+    v.push(4);
+    v.push(5);
+    assert!(v[0] == 72);
+    assert!(v[1] == 2);
+    assert!(v[2] == 3);
+    assert!(v[3] == 4);
+    assert!(v[4] == 5);
+}

tests/kani/Vectors/fixme_763.rs

@@ -0,0 +1,8 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// Failing example from https://github.com/model-checking/kani/issues/763
+fn main() {
+    let x = Vec::<i32>::new();
+    for i in x {}
+}