Animator children duration combination support

[Romel Perez]

The <Animator> component does not have a way to merge itself with its children components to act like it is covering its children flow as one unit. It would imply the parent animator flow duration is the same as the combination of the children components. This feature would simplify the way to combine groups of animators into one for management.

• Add combine: boolean = false prop to enable combination of children animators.
  • If manager = 'parallel', duration.enter and duration.exit are the longest child duration for each case.
  • If manager = 'stagger' or manager = 'sequence', duration.enter is the total duration.
  • If manager is custom function, it is the calculated returned activations duration value.
  • animatorRef.updateDuration() is disabled.
• Add unit tests.