export function openDialogClass() {
  return function <T extends { new(...args: any[]): {} }>(constructor: T) {
    return class extends constructor {
      mat_dialog = inject(MatDialog);
    };
  }
}

@Component({
  selector: 'page',
  templateUrl: 'index.html',
  styleUrls: ['style.scss'],
})

@openDialogClass()
export class Component{ 
    constructor(){
       consol.log(this.mat_dialog) // On angular@14 it's fine, but on angular@15 it's undefined
   }
}

Angular CLI: 15.0.1
Node: 18.12.1
Package Manager: npm 8.19.2
OS: linux x64

Angular: 15.0.1
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... platform-server, router, service-worker

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1500.1
@angular-devkit/build-angular   15.0.1
@angular-devkit/core            15.0.1
@angular-devkit/schematics      15.0.1
@angular/cdk                    15.0.0
@angular/material               15.0.0
@schematics/angular             15.0.1
rxjs                            7.5.7
typescript                      4.8.4