History should be restored only after `RESTORE` tap

### Expected
Once the user has moved the revision slider, tapping/clicking outside the history popover should be similar to `CANCEL`. This is so on iOS, macOS and Electron.

p1615981120005800-slack-C01KRRK0MLJ

### Observed
When the history slider is moved, the note content changes, but the user is still free to tap `CANCEL` or `RESTORE`. Tapping outside the history popover will restore the selected revision:

https://user-images.githubusercontent.com/73365754/111460574-cf371c80-8724-11eb-8812-4913aa80c73c.mp4

### Reproduced
1. Have a note with history available
2. Open revision slider
3. Move the slider so that you can see the difference in note content
4. Tap outside the popover to close it ~> the revision selected with slider will be used.

### Device
Device Make: Samsung
Device Model: A31
Android Version: 10
Simplenote Version: 2.18-rc-1

Start by reproducing the history popover flow on Android with a note that has revisions, then trace the slider, outside-dismissal, CANCEL, and RESTORE handling. Verify that tapping outside leaves the note as CANCEL would and that only RESTORE commits the selected revision.

Written by the indexing model from the issue text.