Replace mode when closing bracket

[nikpappas]

Most of the IDEs and code editors when they match closing brackets they also allow for the closing bracket to be replaced when typed explicitly. I found myself typing double closing brackets and then removing them too often when I realised it was simple enough to implement this new behaviour.

It only affects the current behaviour if:

1. If the editor.completion.auto_close prop is true
2. If the input string is a single character
3. The next character in the text area is exactly the same as the input one.
4. The next character is a closing bracket
5. The previous character is the equivalent opening bracket.

If all those are true then instead of typing in the character the caret moves to the next position.

Closes #6126