Fix RealmSwift List equality

Fix realm#5665 by overriding isEqual for RealmSwift.List to compare elements.

Author: phlippieb

RealmSwift/List.swift

@@ -436,6 +436,14 @@ public final class List<Element: RealmCollectionValue>: ListBase {
     @objc class func _unmanagedArray() -> RLMArray<AnyObject> {
         return Element._rlmArray()
     }
+    
+    public override func isEqual(_ object: Any?) -> Bool {
+        guard let other = object as? List<Element> else { return false }
+        guard self.count == other.count else { return false }
+        
+        return zip(self, other)
+            .reduce(true) { $0 && ($1.0 == $1.1) }
+    }
 }
 
 extension List where Element: MinMaxType {

RealmSwift/Tests/ListTests.swift

@@ -792,4 +792,30 @@ class ListRRCMethodsTests: TestCase {
         array.replaceSubrange(subrange, with: newElements)
         compare(array: array, with: list)
     }
+    
+    func testRealmListOfStringsComparison() {
+        // Lists made from identical arrays should be equal:
+        let strings = ["a", "b", "c"]
+        let list1 = List<String>()
+        list1.append(objectsIn: strings)
+        
+        let list2 = List<String>()
+        list2.append(objectsIn: strings)
+        
+        XCTAssertTrue(list1 !== list2, "instances should not be identical")
+        XCTAssertTrue(list1 == list2, "instances should be equal by `==` operator")
+        XCTAssertTrue(list1.isEqual(list2), "instances should be equal by `isEqual` method")
+        XCTAssertTrue(Array(list1) == Array(list2), "instances converted to Swift.Array should be equal")
+        
+        // Lists made from different-length arrays should not be equal,
+        // even if the common elements are equal.
+        let strings2 = ["a", "b", "c", "d"]
+        let list3 = List<String>()
+        list3.append(objectsIn: strings2)
+        
+        XCTAssertTrue(list1 !== list3, "instances should not be identical")
+        XCTAssertFalse(list1 == list3, "instances should not be equal by `==` operator")
+        XCTAssertFalse(list1.isEqual(list3), "instances should not be equal by `isEqual` method")
+        XCTAssertFalse(Array(list1) == Array(list3), "instances converted to Swift.Array should not be equal")
+    }
 }