ElevationProvider colors are likely half a gridcell off

[asinghvi17]

Consider https://github.com/MakieOrg/Tyler.jl/blob/e67cf5b14daa08106c225341f83e196c3c5fb124/src/tile-plotting.jl#L196-L212

It turns out that image sample points are supposed to lie between elevation sample points. Not a huge deal - but at a high zoom level where you only have one tile it may prove to be very necessary.

Just putting this out there in case anyone is interested in solving it and has free time, this isn't a dealbreaker from my perspective. It might be that we can get away with an adjustment to surface's uv_transform attribute.

cf. https://developers.arcgis.com/documentation/tiled-elevation-service/