Ground clamping broken in 2D and CV

[mramato]

As discussed in #4240

1. Load the KML demo.
2. Switch to 2D
3. Billboards are broken (Similar problems in Columbus View)

May be the same root cause as #4300 and #4062.

We should really fix this before the next release.

[pjcozzi]

We should really fix this before the next release.

+1

[mramato]

I'm about to open a pull request which fixes several clampiing issues, but it turns out that this particular issue is fundamentally a performance problem. If you just sit there and wait forever it eventually finishes and fixes itself. You can also see this by disabling the time slicing (which also makes it go a bit faster). In addition to simply profiling and improving the hot spots, we might need a slightly different approach here in order to keep this acceptably fast (I have some ideas, but I need to experiment some more first).

[mramato]

Also, we disabled billboard clamping by default for KML because of this, so in order to reproduce this you need to set clampToGround to true in the Sandcastle example

[mramato]

I'm removing the "next release" tag since this is no longer the default behavior.