Closing and re-opening keyboard makes old text impossible to backspace on

[HakimMalikOttey]

Steps to reproduce:

1. Install Zefyr and quill_delta
2. Remove everything under TODO: figure out if we need to support autofill in input.dart
3. under toolbar in selection.dart add a double as a field for lastSecondaryTapDownPosition in selection.dart
4. Create a ZefyrScaffold and ZefyrEditor
5. Place text into the field
6. Close the system's keyboard
7. Click on the text that you just created
8. Try backspacing

When installing Zefyr, I used

  zefyr:
    git:
      url: git://github.com/masewo/zefyr.git
      path: packages/zefyr/
      commit: 2e37998

and for quill_delta I used version: ^1.0.1

The reason why I removed everything under autofill and the reason I added a double to lastSecondaryTapDownPosition was because of how, before, whenever I tried running the app without it, the build will fail, saying that I was missing a few arguments. When I went into the selection.dart file, I saw that nothing was being given to lastSecondaryTapDownPosition, so I gave it that number as a placeholder and the app worked. As for the other file, a tutorial told me to just remove it to get rid of the errors.

Besides that, the issue is when I place text into the textfield, close and then reopen the keyboard of my physical android phone, and then try to delete the text I just made using backspace, my app simply won't allow me to do so. I can place more text into the field and delete the new text I created, but anything made before that won't get removed through backspace. It also seems like if I create enough words in the textfield ( 4-5 words) and then try to backspace, some of those words won't get removed at all. That happens even without me closing out the keyboard.

[√] Flutter (Channel stable, 2.0.2, on Microsoft Windows [Version 10.0.18363.1440], locale en-US)
[!] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.
[√] Chrome - develop for the web
[√] Android Studio (version 4.1.0)
[!] Android Studio
    X android-studio-dir = D:\AndroidStudio
    X Unable to determine bundled Java version.
[√] IntelliJ IDEA Community Edition (version 2020.1)
[√] Connected device (3 available)

! Doctor found issues in 2 categories.

[singerdmx]

check out #409 (comment)