Previously, both `ngAnimateSwap` and `ngIf` had a priority of 600, which
meant that (while both are [terminal directives][1]) they were executed
on top of each other (essentially messing each other's comment node).
This commit fixes it, by giving `ngAnimateSwap` a priority of 550, which
is lower than `ngIf` but still higher than other directives.
For reference, here is a list of built-in directive per priority:
```
-400: ngInclude, ngView
-1: ngRef
1: ngMessage, ngMessageDefault, ngMessageExp, ngModel, select
10: ngModelOptions
99: ngHref, ngSrc, ngSrcset
100: attr interpolation, ngChecked, ngDisabled, ngList, ngMax,
ngMaxlength, ngMin, ngMinlength, ngModel (aria), ngMultiple,
ngOpen, ngPattern, ngProp*, ngReadonly, ngRequired, ngSelected,
ngStep, ngValue, option
400: ngInclude, ngView
450: ngInit
500: ngController
600: ngAnimateSwap, ngIf
1000: ngNonBindable, ngRepeat
1200: ngSwitchDefault, ngSwitchWhen
```
[1]: https://docs.angularjs.org/api/ng/service/$compile#-terminal-Fixes#16616Closes#16729
George Kalpakas
3e380325d8