Fix invisible editor overlay issue implementing state restoration capability for page editor

[ceyhun]

Fixes #14674

To test:

1. Start the app from Xcode
2. Go through one of the cases to open page editor

• My Site -> Select site -> Floating + button (bottom right) -> Site page
• My Site -> Select site -> Pages -> + (top right)
• My Site -> Select site -> Pages -> Select any page to edit
• My Site -> Select site -> Pages -> Search -> Select any page to edit
• Press home button -> Pull down to search in Spotlight -> search the name of a draft page -> select to open the app and see the editor

3. Background app using the Home button
4. Stop the debugger in Xcode ⚠️ Do not use the app switcher to force quit it during debugging. The system automatically deletes its preserved state when the user force quits the app. See here to learn more.
5. Launch the app again using Xcode (Now UIKit initiates the state restoration process)
6. Expect page editor to be shown from where it left off

Deep link test:

1. Need to change build configuration to Release-Internal for this to work (Changing only the scheme to WordPress Internal won't work, need to "Edit Scheme..." and modify the "Build Configuration" as well)
2. Start the app from Xcode
3. Background app using the Home button
4. Run in terminal xcrun simctl openurl booted "https://apps.wordpress.com/get#/page"
5. App should open with the editor to create a new page
6. Background app using the Home button
7. Stop the debugger in Xcode
8. Launch the app again
9. Expect page editor to be shown from where it left off

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading it from AppCenter here with build number: 35604. IPA is available here. If you need access to this, you can ask a maintainer to add you.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[chipsnyder]

Nice job tracking down this fix @ceyhun!

The flows look good to me. I also tested a few cases related to Modal Layout Picker:

To disable or enable the development version of Modal Layout Picker

• Open the app from the build that allows FeatureFlags such as a PR build or a local development build
  • By default, the modal layout picker will be disabled.
  • From the site page:
    • Click on your Gravatar.
    • Click on App Settings.
    • Click on Debug.
    • Toggle "Gutenberg Modal Layout Picker" to enable or disable the picker
      

1. Turn on the Modal Layout Picker feature
2. Open the editor by:
   • Select FAB icon -> Site Page -> Create Blank Page
   • Select FAB icon -> Site Page -> Select a layout -> Create Page
   • Select FAB icon -> Site Page -> Create Blank Page
   • Select FAB icon -> Site Page -> choose a layout -> Create Page
   • Select FAB icon -> Site Page -> choose a layout -> Preview -> Create Page
   • Select Pages -> Select the ➕ -> Create Blank Page
   • Select Pages -> Select the ➕-> Select a layout -> Create Page
   • Select Pages -> Select the ➕ -> Create Blank Page
   • Select Pages -> Select the ➕ -> choose a layout -> Create Page
   • Select Pages -> Select the ➕ -> choose a layout -> Preview -> Create Page
3. Follow the reset of the steps from the above starting at step 3

[ceyhun]

Thanks for testing the extra cases @chipsnyder 🙇‍♂️