fix(virtual-repeat): handle array changes correctly

[AStoker]

Resolves: #106, #98, #89, #87, #60
Previous behavior did not handle array changes correctly (in particular
changes with the size of the array). Behavior now allows for array
changes with different sizes, and should keep appropriate scroll
positions.

[AStoker]

This is an initial PR to test out functionality. I'd like for a few others to look at it to confirm it works for them in their use cases before merging.
@altenstedt, could you try and pull down this PR and test it out?
@EisenbergEffect, when you have a minute, if you could give the code a look over as well.
I'm out for the weekend, but I wanted to get something out for review as soon as I could. That being said, I'd like to make the tests a bit more robust, and I'll have that in a separate commit on Monday (most likely).

[altenstedt]

I have tested your PR on our code and it looks good. I have had no issues so far. Looks like this resolves at least #106.

[AStoker]

@altenstedt, so this looks good except for tables right now. The way that we have buffer elements outside the table element has been bothering me for a while, and it starts to interfere here when we are recalculating heights (initial issue that caused buffer elements to be moved: #46).
In regards to the other issues, I'm still doing some testing, but they may require a separate commit. I know at least #89 should be solved, #87 and #98 still require more testing to confirm. I'll be working on it tonight though.

[altenstedt]

We do not use virtual-repeat.for with tables, so that's why I have not seen issues related to tables.

[AStoker]

Sounds good. I just want to make sure that I don't break anything more than it already is, I can come back later and fix up the table strategy.

[AStoker]

@altenstedt, made a few modifications to help tables be a bit more graceful (there's work to be done, as they're messed up as is, but the last commit should help). Just want to make sure it's still working for you with the changes though.

[AStoker]

@EisenbergEffect, I think we're good for a review. These commits fixed a lot of bugs (as is the case when something is still in beta, as this tool is). Tests are all passing, and I tested a bunch of different use cases on my machine, hopefully I covered all the bases (but there's always the edge cases).
We will need to address some of the table rendering issues eventually (probably going to need some help from @martingust to explain a few changes made last year).

[EisenbergEffect]

@AStoker You know more about the virtualization implementation than I do at this point :) If you feel good about it, go ahead and merge. Let me know when it's ready and I'll get a release out. Thanks for the hard work!

[EisenbergEffect]

@martingust If you have a chance to look at this, that would be great. Thanks!

[AStoker]

Well, let's give this a whirl :) We're in Beta for a reason

[AStoker]

@EisenbergEffect, ready as we'll ever be for a release :)