Refactoring of lib

Breaking Change

• Converted muliselect.service to utitility function
• If you have used multiselect.service.ts inside your code, import the specific function from import directictly
  • For eg. if you have this.multiselectService.closest() inside your code. Replace it with closest function

    import {MultiselectService} from '@ngx-lib/multiselect';
  
    // somewhere you might have used
    this.multiselectService.closest(el);
  
    // change it to
    import {closest} from '@ngx-lib/multiselect';
  
    closest(el);