[mat-tree] Nodes are not updated correctly with trackyBy function set

#### Bug, feature request, or proposal:
MatTree does not reflect the changes to the nodes if trackBy function is used. For example, I have several items with trackBy function pointing to their "id" property. If I provide a new array with completely same ids, but with changes to some of the other properties, change detection does not occur.

#### What is the expected behavior?
When used with trackBy function MatTree should trigger change detection on all nodes, just like ngFor with trackBy does.

#### What is the current behavior?
No changes are detected therefore data is not updated in template.

#### What are the steps to reproduce?
https://stackblitz.com/edit/angular-material2-issue-z8ubtt

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Latest versions of Angular, Material (check StackBlitz). Any browser.

#### Is there anything else we should know?
Same [issue](https://github.com/angular/material2/issues/7877) was observed last year with MatTable.

Inizia con la riproduzione StackBlitz collegata e confronta il comportamento di MatTree con ngFor quando viene utilizzata una funzione trackBy. Esamina la issue correlata #7877 e verifica che la sostituzione dell'array di nodi aggiorni le proprietà modificate nel template renderizzato preservando i nodi tracciati.

Scritto dal modello di indicizzazione a partire dal testo della issue.