[Rust] Shared String (#6367)

* Adds shared strings and tests for shared strings

* Adds resets on string_map

* Moved shared strings to use vector instead of hashmap

* Addresses all the issues

* Resolves some comments

tests/rust_usage_test/tests/integration_test.rs

@@ -3051,4 +3051,51 @@ fn load_file(filename: &str) -> Result<Vec<u8>, std::io::Error> {
     f.read_to_end(&mut buf)?;
     Ok(buf)
 }
+
+#[test]
+fn test_shared_strings() {
+    let mut builder = flatbuffers::FlatBufferBuilder::new();
+    let offset1 = builder.create_shared_string("welcome to flatbuffers!!");
+    let offset2 = builder.create_shared_string("welcome");
+    let offset3 = builder.create_shared_string("welcome to flatbuffers!!");
+    assert_ne!(offset2.value(), offset3.value());
+    assert_eq!(offset1.value(), offset3.value());
+    builder.reset();
+    let offset4 = builder.create_shared_string("welcome");
+    let offset5 = builder.create_shared_string("welcome to flatbuffers!!");
+    assert_ne!(offset2.value(), offset4.value());
+    assert_ne!(offset5.value(), offset1.value());
+    builder.reset();
+
+    // Checks if the shared string function would always work with
+    // an object in between the writes
+    let name = builder.create_shared_string("foo");
+    let enemy = my_game::example::Monster::create(&mut builder, &my_game::example::MonsterArgs {
+        name: Some(name),
+        ..Default::default()
+    });
+    let secondary_name = builder.create_shared_string("foo");
+    assert_eq!(name.value(), secondary_name.value());
+
+    // Builds a new monster object and embeds enemy into it so we can verify
+    // that shared strings are working.
+    let args = my_game::example::MonsterArgs {
+        name: Some(secondary_name),
+        enemy: Some(enemy),
+        testarrayofstring: Some(builder.create_vector(&[name, secondary_name])),
+        ..Default::default()
+    };
+    // Building secondary monster
+    let main_monster = my_game::example::Monster::create(&mut builder, &args);
+    builder.finish(main_monster, None);
+    let monster = my_game::example::root_as_monster(builder.finished_data()).unwrap();
+
+    // Checks if the embedded object (Enemy) name is foo
+    assert_eq!(monster.enemy().unwrap().name(), "foo");
+    let string_vector = monster.testarrayofstring().unwrap();
+    // Check if the vector will have the same string
+    assert_eq!(string_vector.get(0), "foo");
+    assert_eq!(string_vector.get(1), "foo");
+}
+
 }