Lifecycle events called in wrong order

# Bug Report

**Ionic version:**
[x] **4.0.0**

**Current behavior:**
When changing the root page the lifecycle events of the previous and next page seem to fire out of order. So, lets say page A is currently displayed. Navigating to page B fires the lifecycle events in the following order:
1. Page B: ngOnInit
2. Page B: ionViewWillEnter
3. Page B: ionViewDidEnter
4. Page A: ngOnDestroy

(ionViewWillLeave and ionViewDidLeave do not fire at all)

**Expected behavior:**
I would expect that page A fires ngOnDestroy or ionViewWillLeave or ionViewDidLeave before page B's 'enter' events