Add copy button feedback

Signal/src/ViewControllers/Registration/OnboardingPublicKeyViewController.swift

@@ -17,6 +17,12 @@ final class OnboardingPublicKeyViewController : OnboardingBaseViewController {
         return result
     }()
 
+    private lazy var copyButton: OWSFlatButton = {
+        let result = createLinkButton(title: NSLocalizedString("Copy", comment: ""), selector: #selector(copyMnemonic))
+        result.accessibilityIdentifier = "onboarding.publicKeyStep.copyButton"
+        return result
+    }()
+    
     init(onboardingController: OnboardingController, userName: String?) {
         super.init(onboardingController: onboardingController)
         self.userName = userName
@@ -76,6 +82,14 @@ final class OnboardingPublicKeyViewController : OnboardingBaseViewController {
 
     @objc private func copyMnemonic() {
         UIPasteboard.general.string = mnemonic
+        copyButton.isUserInteractionEnabled = false
+        copyButton.setTitle(title: NSLocalizedString("Copied ✓", comment: ""), font: .ows_dynamicTypeBodyClamped, titleColor: .ows_materialBlue)
+        Timer.scheduledTimer(timeInterval: 4, target: self, selector: #selector(enableCopyButton), userInfo: nil, repeats: false)
+    }
+
+    @objc private func enableCopyButton() {
+        copyButton.isUserInteractionEnabled = true
+        copyButton.setTitle(title: NSLocalizedString("Copy", comment: ""), font: .ows_dynamicTypeBodyClamped, titleColor: .ows_materialBlue)
     }
 
     @objc private func register() {

Signal/translations/en.lproj/Localizable.strings

@@ -2553,4 +2553,5 @@
 "Password (Optional)" = "Password (Optional)";
 "Please save the seed below in a safe location. It can be used to restore your account if you lose access, or to migrate to a new device." = "Please save the seed below in a safe location. It can be used to restore your account if you lose access, or to migrate to a new device.";
 "Copy" = "Copy";
+"Copied ✓" = "Copied ✓";
 "Register" = "Register";