[FeatureHighlight] Add swift example (#4439)

Added a feature highlight swift example. Also, attempted to reproduce #3644 but found that the bug had already been resolved.

components/FeatureHighlight/examples/FeatureHightlightTypicalUseViewController.swift

@@ -0,0 +1,75 @@
+/*
+ Copyright 2018-present the Material Components for iOS authors. All Rights Reserved.
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+
+import MaterialComponents
+
+/// Example to show how to use a feature highlight
+class FeatureHighlightSwiftViewController: UIViewController {
+
+  let showButton = MDCButton()
+  let featureButton = MDCButton()
+  var colorScheme = MDCSemanticColorScheme()
+  var typographyScheme = MDCTypographyScheme()
+  let buttonScheme = MDCButtonScheme()
+
+  override func viewDidLoad() {
+    super.viewDidLoad()
+    colorScheme.backgroundColor = .white
+    view.backgroundColor = colorScheme.backgroundColor
+
+    showButton.setTitle("Show Feature Highlight", for: .normal)
+    showButton.addTarget(self, action: #selector(showFeatureHighlight), for: .touchUpInside)
+    MDCContainedButtonThemer.applyScheme(buttonScheme, to: showButton)
+    self.view.addSubview(showButton)
+
+    featureButton.setTitle("Feature", for: .normal)
+    MDCContainedButtonThemer.applyScheme(buttonScheme, to: featureButton)
+    self.view.addSubview(featureButton)
+  }
+
+  override func viewDidLayoutSubviews() {
+    super.viewDidLayoutSubviews()
+    showButton.sizeToFit()
+    showButton.frame.origin.y =
+      view.bounds.height - (showButton.frame.height + 60)
+    showButton.frame.origin.x = view.center.x - showButton.frame.width / 2
+
+    featureButton.sizeToFit()
+    featureButton.frame.origin.x = view.center.x - featureButton.frame.width / 2
+    featureButton.frame.origin.y = view.bounds.height / 2 - featureButton.frame.height / 2
+  }
+
+  func showFeatureHighlight() {
+    let vc = MDCFeatureHighlightViewController(highlightedView: featureButton,
+                                               completion: nil)
+    MDCFeatureHighlightColorThemer.applySemanticColorScheme(colorScheme, to: vc)
+    MDCFeatureHighlightTypographyThemer.applyTypographyScheme(typographyScheme, to: vc)
+    vc.mdc_adjustsFontForContentSizeCategory = true
+    vc.titleText = "Hey this is a title for the Feature Highlight"
+    vc.bodyText = "This is the description of the feature highlight view controller"
+    self.present(vc, animated: true, completion: nil)
+  }
+}
+
+extension FeatureHighlightSwiftViewController {
+  class func catalogBreadcrumbs() -> [String] {
+    return ["Feature Highlight", "Feature Highlight (Swift)"]
+  }
+
+  class func catalogIsPrimaryDemo() -> Bool {
+    return false
+  }
+}