fix(toast): export NgbToastModule publicly (#3259)
fix(toast): export NgbToastModule publicly (#3259)

Main export of NgbToastModule was missing, which basically prevented
people to write

```typescript
import {NgbToastModule} from "@ng-bootstrap/ng-bootstrap";
```

Fixes #3258
jnizet/ng-bootstrap,fbasso/ng-bootstrap,maxokorokov/core,jnizet/ng-bootstrap,jnizet/ng-bootstrap,benouat/ng-bootstrap,ng-bootstrap/ng-bootstrap,maxokorokov/core,ng-bootstrap/ng-bootstrap,ng-bootstrap/ng-bootstrap,ng-bootstrap/ng-bootstrap,fbasso/ng-bootstrap,benouat/ng-bootstrap,benouat/ng-bootstrap,maxokorokov/core,benouat/ng-bootstrap,fbasso/ng-bootstrap,fbasso/ng-bootstrap,jnizet/ng-bootstrap,maxokorokov/core