[android] add support for mapzen terrarium raster-dem encoding

[mollymerp]

remaining tail work from #11224

basically just guessed here, so if there's more to be done please let me know @tobrun

[jfirebaugh]

If this is intended to be included in boba, please retarget it at release-boba. 🙏

[tobrun]

Thank you for this @mollymerp, to review I will write a small test around this.

[LukasPaczos]

To validate this PR I used Amazon's tile server: https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/{x}/{y}.png. Results below.

With mapbox encoding:

With terrarium encoding:

Looks like we are good here @tobrun.

[mollymerp]

thank you @LukasPaczos @tobrun !