Add zRange prop to TileLayer for use with TerrainLayer

[kylebarron]

Closes #4347

(Mt. Rainier, ~4000m; no missing tiles)

Change List

• Adds a zRange prop to TileLayer, which is passed down to viewport.unproject to find tile indices given a range of elevations (in meters).
• Updates TerrainLayer's zRange state on viewport load, calculated as the minimum and maximum of all triangle mesh heights. It does seem a little excessive to scan all mesh heights on every viewport change, so I'm open to ideas about more efficient z range calculation.

[CLAassistant]

All committers have signed the CLA.

[ibgreen]

Side note: The long term solution for this might be to simply generate bounding boxes/volumes for each tile and then use frustum intersection logic implemented for 3D tiles. This aligns with our ambition to gradually unify the tile layers layers.

[Pessimistress]

CI is failing - You can run yarn test node locally to see the errors.

[kylebarron]

When I run tests locally on master, I get an unrelated gl error. I've run npm run bootstrap though, so I'm not sure why this is happening

Running node tests...
deck: deck.gl untranspiled source - set deck.log.level=1 (or higher) to trace attribute updates
/Users/kyle/github/mapping/deck.gl/test/node.js:30
canvas.width = gl.drawingBufferWidth;
                  ^

TypeError: Cannot read property 'drawingBufferWidth' of null
    at Object.<anonymous> (/Users/kyle/github/mapping/deck.gl/test/node.js:30:19)
    at Module._compile (internal/modules/cjs/loader.js:959:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)
    at Module.load (internal/modules/cjs/loader.js:815:32)
    at Function.Module._load (internal/modules/cjs/loader.js:727:14)
    at Module.require (internal/modules/cjs/loader.js:852:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (/Users/kyle/github/mapping/deck.gl/node_modules/ocular-dev-tools/node/test.js:45:5)
    at Module._compile (internal/modules/cjs/loader.js:959:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)

From travis it looks like the main error is

not ok 3268 non-geospatial with tile size
  ---
    operator: deepEqual
    expected: |-
      [ '1,2,3', '1,3,3', '2,2,3', '2,3,3', '3,2,3', '3,3,3', '4,2,3', '4,3,3' ]
    actual: |-
      [ '0,1,3', '1,1,3', '2,1,3' ]
    stack: |-
      Error: non-geospatial with tile size

I'm still working on figuring out how these changes caused that.

[Pessimistress]

Ah. headless-gl does not work with node.js>12.12.

[kylebarron]

I switched to node 10 and can run the tests locally now. I think there were two errors, and I fixed one but not the other yet.

[coveralls]

Coverage decreased (-0.06%) to 80.633% when pulling 1985a37 on kylebarron:terrain-tiles-viewport into a5545e7 on uber:master.

[kylebarron]

I fixed failing tests but didn't add a zRange test. I could add tests that check against the current getTileIndices output, but I'm not sure I'd be able to independently compute the correctness of that output.