UI: add containing View for each Label

`WC_STATIC` control doesn't receive events like `WM_CONTEXTMENU`. To be able to handle those events, let's create containing views for `WC_STATIC` instances.

Co-authored-by: Saleem Abdulrasool <compnerd@compnerd.org>

Author: egorzhdan

Sources/SwiftWin32/Views and Controls/Label.swift

@@ -20,22 +20,53 @@ private let SwiftLabelProc: SUBCLASSPROC = { (hWnd, uMsg, wParam, lParam, uIdSub
   return DefSubclassProc(hWnd, uMsg, wParam, lParam)
 }
 
-public class Label: Control {
+fileprivate class LabelView: View {
   private static let `class`: WindowClass = WindowClass(named: WC_STATIC)
-  private static let style: WindowStyle = (base: WS_TABSTOP | DWORD(SS_NOTIFY), extended: 0)
+  private static let style: WindowStyle = (base: 0, extended: 0)
+
+  @_Win32WindowText
+  public var text: String?
+
+  public init(frame: Rect) {
+    super.init(frame: frame, class: LabelView.class, style: LabelView.style)
+  }
+}
+
+public class Label: Control {
+  private static let `class`: WindowClass =
+      WindowClass(hInst: GetModuleHandleW(nil), name: "Swift.Label")
+  private static let style: WindowStyle = (base: WS_TABSTOP, extended: 0)
+
+  private let view: LabelView
+
+  public override var frame: Rect {
+    didSet {
+      self.view.frame = Rect(origin: .zero, size: frame.size)
+    }
+  }
 
   public override var font: Font! {
-    get { return super.font }
-    set(value) { super.font = value }
+    get { return self.view.font }
+    set(value) { self.view.font = value }
   }
 
-  @_Win32WindowText
-  public var text: String?
+  public var text: String? {
+    get { return self.view.text }
+    set(value) { self.view.text = value }
+  }
+
+  public override var subviews: [View] {
+    get {
+      return super.subviews.filter { $0 !== view }
+    }
+  }
 
   public init(frame: Rect) {
+    self.view = LabelView(frame: Rect(origin: .zero, size: frame.size))
     super.init(frame: frame, class: Label.class, style: Label.style)
     _ = SetWindowSubclass(hWnd, SwiftLabelProc, UINT_PTR(1),
                          unsafeBitCast(self as AnyObject, to: DWORD_PTR.self))
+    self.addSubview(self.view)
   }
 
   // ContentSizeCategoryAdjusting