Allow commands with prefixes to be sticky

[EtiamNullam]

I'm opening this issue because:

• I'll report a bug
• I'll propose a new feature

Description

I think it would be nice if there was an option like suggested in #707 but for most (if not all) other options with prefix.

I have many prefixes in my neovim made sticky and I think it works just great.

Example

Good example would be zooming out and in. Often when adjusting zoom you don't exactly know which value will be the best or number of steps might be difficult to guess, so you have to invoke it several times, like zizizizizi (to zoom in 5 times).

I'm proposing instead that z could be sticky so after you press zi you're still at z, so you can just press ziiiii (to zoom in 5 times).

There is still a question how to leave this "sub-mode", I think both <Enter> and <Esc> would fit.