NbIconLibraries RegisterFontPack cant understand (nb-icon eva)

### Issue type

**I'm submitting a ...**

* [ ] bug report
* [ X ] feature request

### Issue description

**Current behavior:**
I'm trying migrate from v3.* to v4 and cant understand how create a pack of icons for eva-icon (nb-icon component).

I have two style files with font-icons, how can registerFontPack with a font-family name and listo of icon's name?

**Expected behavior:**
Create a FontPack type:font

**Steps to reproduce:**
i'm using this function:
```
let ecommerce_icons = [
{"025-cashbox": "\f100"}
]
this.iconLibraries.registerFontPack('ecommerce', { font: 'Ecommerce', icons: ecommerce_icons , iconClassPrefix: 'ecommerce' });
```

Thanks!