CARTO: Improve H3Tileset2D.getTileIndices() by adding buffer

[felixpalmer]

Background

Due to h3.polygonToCells polyfilling base on cell centers, H3Tileset2D.getTileIndices() sometimes misses cells near the edges of the viewport. Previously the code would sample at a higher h3 level, but even this would sometimes miss cells.

Without padding:

With padding:

Change List

• Add padBoundingBox function to increase bounds by size of cell
• Reduce oversampling
• Fix east/west mixup
• Test update

[coveralls]

coverage: 90.002% (+0.006%) from 89.996%
when pulling 9bbd05c on felix/h3-buffer
into 5ad2534 on master.

[donmccurdy]

Nice improvement!