[Feature Request] Let change modal icons.

[Rid1FZ]

Is your feature request related to a problem? Please describe.
There are 3 options to set 3 different types of icons for evil-mode, but it is not enough customizable. It will always use some rounded nerd-fonts icons, or unicode icon, or text. An option to use any custom icon will be a great deal.

Describe the solution you'd like
I went through the source code and found that the doom-modeline--evil function is used to set the icons in doom-modeline-segments.el file. Checking if doom-modeline--evil is already defined will let us define this function(hence customize the icons) before loading doom-modeline.

Additional context
I tried defining this function before and after loading doom-modeline, but it didn't did the trick. I think some changes needed in source code as well.

[seagle0128]

doom-modeline--evil is an inline function.

[Rid1FZ]

@seagle0128 we can also use variables like doom-modeline-evil-normal-icon or something. It is much better compared to re-defining any builting function outside of the package.