Add support for Angular 18

[icjmaa]

Hello,

I'm currently using the ngx-toastr library in my Angular project and I noticed that it doesn't support Angular 18 yet. I would like to request an update to the library to add support for Angular 18.

I believe that many users of ngx-toastr would greatly benefit from having Angular 18 support, as it provides new features and improvements to the framework. It would be great if the library could be updated soon to support the latest version of Angular.