refactor(dialog): remove custom injector usage (#18565)

Replaces the usage of our custom `PortalInjector` with Angular's `Injector`. The advantage of using the default one is that the injection logic is consistent with everything else and we don't have to require users to polyfill `WeakMap`.

The idea here is to eventually replace all usages of `PortalInjector` with `Injector` and to deprecate it, but I wanted to try it out against `dialog` since it's probably the most used and well tested of the components that are using the custom injector.

(cherry picked from commit ff8d56e)

Author: crisbeto

src/material/dialog/dialog.ts

@@ -14,7 +14,7 @@ import {
   OverlayRef,
   ScrollStrategy,
 } from '@angular/cdk/overlay';
-import {ComponentPortal, ComponentType, PortalInjector, TemplatePortal} from '@angular/cdk/portal';
+import {ComponentPortal, ComponentType, TemplatePortal} from '@angular/cdk/portal';
 import {Location} from '@angular/common';
 import {
   Inject,
@@ -25,6 +25,7 @@ import {
   Optional,
   SkipSelf,
   TemplateRef,
+  StaticProvider,
 } from '@angular/core';
 import {defer, Observable, of as observableOf, Subject} from 'rxjs';
 import {startWith} from 'rxjs/operators';
@@ -215,9 +216,11 @@ export class MatDialog implements OnDestroy {
    */
   private _attachDialogContainer(overlay: OverlayRef, config: MatDialogConfig): MatDialogContainer {
     const userInjector = config && config.viewContainerRef && config.viewContainerRef.injector;
-    const injector = new PortalInjector(userInjector || this._injector, new WeakMap([
-      [MatDialogConfig, config]
-    ]));
+    const injector = Injector.create({
+      parent: userInjector || this._injector,
+      providers: [{provide: MatDialogConfig, useValue: config}]
+    });
+
     const containerPortal = new ComponentPortal(MatDialogContainer,
         config.viewContainerRef, injector, config.componentFactoryResolver);
     const containerRef = overlay.attach<MatDialogContainer>(containerPortal);
@@ -283,29 +286,29 @@ export class MatDialog implements OnDestroy {
   private _createInjector<T>(
       config: MatDialogConfig,
       dialogRef: MatDialogRef<T>,
-      dialogContainer: MatDialogContainer): PortalInjector {
+      dialogContainer: MatDialogContainer): Injector {
 
     const userInjector = config && config.viewContainerRef && config.viewContainerRef.injector;
 
     // The MatDialogContainer is injected in the portal as the MatDialogContainer and the dialog's
     // content are created out of the same ViewContainerRef and as such, are siblings for injector
     // purposes. To allow the hierarchy that is expected, the MatDialogContainer is explicitly
     // added to the injection tokens.
-    const injectionTokens = new WeakMap<any, any>([
-      [MatDialogContainer, dialogContainer],
-      [MAT_DIALOG_DATA, config.data],
-      [MatDialogRef, dialogRef]
-    ]);
+    const providers: StaticProvider[] = [
+      {provide: MatDialogContainer, useValue: dialogContainer},
+      {provide: MAT_DIALOG_DATA, useValue: config.data},
+      {provide: MatDialogRef, useValue: dialogRef}
+    ];
 
     if (config.direction &&
         (!userInjector || !userInjector.get<Directionality | null>(Directionality, null))) {
-      injectionTokens.set(Directionality, {
-        value: config.direction,
-        change: observableOf()
+      providers.push({
+        provide: Directionality,
+        useValue: {value: config.direction, change: observableOf()}
       });
     }
 
-    return new PortalInjector(userInjector || this._injector, injectionTokens);
+    return Injector.create({parent: userInjector || this._injector, providers});
   }
 
   /**