fix($parse): one-time binding for literal expressions works as expected

[rodyhaddad]

Meaning the watcher is only removed when all the properties of the object, or
all the elements of the array, are defined.

Closes #7663

[mary-poppins]

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[Narretz]

👍 😺

[lgalfaso]

I think I understand why there is a need for this change, but I see two minor nits that need to be discussed
1/ It is arbitrary that the check is only on one level, e.g the expression '::[{abc: abc}]'
2/ The expressions '::[abc: abc]' and '::true ? [abc: abc] : false' work differently

[Narretz]

@rodyhaddad Do you know what the status of this is?

Regarding point 1, I think since this is mainly mimicking bindonce, it's simply a decision made by convention to only support one level. More complex bindings are proably very rare.

[rodyhaddad]

Mentioning this to Igor, this change is more for ng-style and ng-class than anything else.
So supporting nested literal expressions doesn't make much sense. Specially since it would require a big rewrite of $parse.

If someone has a complex expression and still wants to make use of one-time binding for objects/array, they can always wait till everything is defined before setting a variable on the $scope