feat(Apply): create protocol

Sources/HelperKit/Protocols/Apply.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+public protocol Apply {}
+
+public extension Apply where Self: AnyObject {
+    /// Calls the closure with `self` as its argument and returns `self`.
+    ///
+    ///     let button = UIButton(type: .system).apply {
+    ///         $0.setTitleColor(.black, for: .normal)
+    ///         $0.setTitleColor(.gray, for: .disabled)
+    ///     }
+    @inlinable func apply(closure: (Self) -> Void) -> Self {
+        closure(self)
+        return self
+    }
+}
+
+extension NSObject: Apply {}