Selection's range.index is incorrect on navigation to right side of an embed

[ryan-wheatley]

See a short video

https://www.youtube.com/watch?v=Hlu5Z5wTwdc

To reproduce

• Go to https://quilljs.com/playground/snow and add the 'formula' embed to the toolbar.
• Create an embed formula blot with the word 'example'.
• Ensure there is text before, after, and on the line below the embed.
• Navigate the the cursor line below, just under the right-hand side of the embed.
• Use the arrow up key to move the cursor to the end of the embed.
• Press the right arrow key, or insert a character. Observe the behavior.
• This can also be replicated by using the mouse to put the cursor at the end of the embed.

Expected Behavior

When navigating to the end of an embed in this way,

• The right arrow should move the cursor forward one.
• The inserted character should have the cursor after it.

Actual Behavior

• The right arrow key does noting on the first keypress, then works as normal.
• If instead you insert text, when the first character is inserted the cursor remains at the end of the embed.

On investigation

The 'selection-change' event cause by arrowing up to the end of the embed returns a range.index that is equal to the start of the embed, not the end. When you press the right arrow key, the cursor wont move, but 'selection-change' will then return the correct range.index.

If you use the arrow keys while staying on the same line, this bug wont happen (and range.index is correct as you go left and right of the embed).

The bug behaviour is quite frustrating for users when navigating, any help would be greatly appreciated!

Platform MacOS
Quill Version 2.0.0-rc.5