Lowered required macOS version to 10.11 for the module by back-porting "CollectionDifference" related methods

Renamed collection difference methods to avoid clashes on macOS 10.15+

Author: guidedways

Package.swift

@@ -3,8 +3,11 @@ import PackageDescription
 
 let package = Package(
   name: "OutlineViewDiffableDataSource",
-  platforms: [.macOS(.v10_15)],
+  platforms: [.macOS(.v10_11)],
   products: [.library(name: "OutlineViewDiffableDataSource", targets: ["OutlineViewDiffableDataSource"])],
+  dependencies: [
+    // Dependencies declare other packages that this package depends on.
+  ],
   targets: [
     .target(name: "OutlineViewDiffableDataSource", dependencies: [], path: "Sources"),
     .testTarget(name: "OutlineViewDiffableDataSourceTests", dependencies: ["OutlineViewDiffableDataSource"], path: "Tests"),