Ignore empty tile 's SSE when refining tile

[baothientran]

We got a support issue where the tileset has some of the empty tiles that are near the leaf of the tree. These tiles usually have low SSE, which prevents the current tile from refining further. It is unfortunate that we have to ignore empty tile's SSE and traverse down the tree until we meet a tile that has content available to render.

@lilleyse Can you please take a look at it? Please let me know if I should add anything

[cesium-concierge]

Thanks for the pull request @baothientran!

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[baothientran]

Since we ignore the empty tile, I notice there is a different behavior in the tileset that has mix add-replacement refinement. This is the sandcastle example.

Below is the tree of the tileset

                C(Replace)
     E(ADD)                    E(ADD)
C                C            C               C

In the master branch, when we zoom in, the content leaf tile is iteratively render. But in this branch, they are rendered all at once

Master branch:

This PR:

[cesium-concierge]

Thanks again for your contribution @baothientran!

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[cesium-concierge]

Thanks again for your contribution @baothientran!

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[lilleyse]

I think we should close this and instead focus on addressing #9356

There are three different ways that we're refining empty tiles

• Don't treat empty tiles as special. If empty tiles exist they may be selected and appear as holes. (Current Cesium Native behavior, and most spec compliant)
• Skip empty tiles during refinement that meet the SSE. (Current CesiumJS behavior)
• Skip empty tiles during refinement regardless of whether they meet the SSE. (This PR)