[MD UI] 'Eye' icon availability is synced with actual MD status only when note text is updated

### Expected
Eye icon should be shown if note has MD enabled
Eye icon should be hidden is note has MD disabled

### Observed
Case when 'Markdown' is checked (enabled) in note menu, but there's no eye icon. See video.

### Reproduced
See video.

1. macOS: Create a new note with some text. Pay attention to eye icon availability being consistent with 'Markdown' being enabled/disabled in note menu
2. iPhone: change the MD state
3. macOS: check the MD state via note menu ~> you will see that state is actual (correct and synced), but eye icon is not displayed accordingly. As soon as you start typing, eye icon will get the correct display status.

https://user-images.githubusercontent.com/73365754/105345326-cb878d80-5bec-11eb-9605-6a03f5ff9887.mov

Make|Model|macOS Version|App Version
-|-|-|-
Mac|MBP 15 "|10.15.7|2.6
iPhone|XR|14.3|4.30

Start by reproducing the macOS and iPhone steps, then inspect the Markdown note-menu state and the macOS eye-icon availability after the Markdown state changes remotely. Done means the eye icon is shown whenever Markdown is enabled and hidden whenever it is disabled, without requiring note text to be edited.

Written by the indexing model from the issue text.