ConfirmDialog appendTo is broken

[slinlee]

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Plunkr Case (Bug Reports)
https://stackblitz.com/edit/github-knoa7y?file=src/app/app.component.html

Current behavior
Click the button to open the confirmation dialog. Notice that:

• No modal backdrop
• The dialog is positioned inline and not on top of anything
• The console shows the error:

ERROR TypeError: "this.el.nativeElement.children[0] is undefined"
primeng6.1.0/components/confirmdialog/confirmdialog.js:133:9primeng6.1.0/components/confirmdialog/confirmdialog.js:65:17View_ConfirmDialog_1ng:///ConfirmDialogModule/ConfirmDialog.ngfactory.js:129:23core6.1.2/bundles/core.umd.js:10277:20core6.1.2/bundles/core.umd.js:11370:26core6.1.2/bundles/core.umd.js:11073:16core6.1.2/bundles/core.umd.js:7736:20core6.1.2/bundles/core.umd.js:8180:42browser6.1.2/bundles/platform-browser-animations.umd.js:220:29browser6.1.2/bundles/platform-browser-animations.umd.js:218:25js0.8.26/dist/zone.js:388:17core6.1.2/bundles/core.umd.js:3882:28js0.8.26/dist/zone.js:387:17js0.8.26/dist/zone.js:138:24core6.1.2/bundles/core.umd.js:3796:20browser6.1.2/bundles/platform-browser-animations.umd.js:217:21js0.8.26/dist/zone.js:388:17js0.8.26/dist/zone.js:138:24js0.8.26/dist/zone.js:872:29js0.8.26/dist/zone.js:421:17js0.8.26/dist/zone.js:188:28js0.8.26/dist/zone.js:595:25js0.8.26/dist/zone.js:500:21js0.8.26/dist/zone.js:1540:9js0.8.26

Expected behavior
At least in version 6.0.0, the dialog would be shown on a modal backdrop, on top of all other elements on screen, and no errors would be displayed in the console.

Minimal reproduction of the problem with instructions
Use the instructions with the Plunkr below
https://stackblitz.com/edit/github-knoa7y?file=src/app/app.component.html

• PrimeNG version: 6.1.2
  This could be related to 3491a64#r30214919

• Browser: All