Add REMOVE and INSERT to eager options

[uNmAnNeR]

Discussed in https://github.com/uNmAnNeR/imaskjs/discussions/703

^{Originally posted by mattstobbs July 27, 2022} Hey, I'm using a simple mask of '0000 0000'. It works great when typing numbers but when the backspace is clicked, if there are only four numbers left, there is a trailing space. For example

"1234"
{Click 5}
"1234 5"
{Backspace}
"1234 "

Is there a way to remove the trailing space on backspace?