refine reconciliation algorithm of array

[liuqiang1357]

When I assign a array node with structural equalled values, nothing have been changed, but the observer of array is still called. I think this may cause some performance problem.

also fix issue: #928

[mweststrate]

Hi @liuqiang1357 can you introduce some unit tests to demonstrate what problems this fixes? I think this PR might violate some internal assumptions so far, but not entirely sure yet :)

[liuqiang1357]

Hi @mweststrate I have added unit tests for this.

[xaviergonz]

@liuqiang1357 does this also solve unshifting as mentioned in the last comment of #928?

[liuqiang1357]

@xaviergonz Yes, you can see it in the unit test.

[mweststrate]

Thanks a lot @liuqiang1357, looking good!