Map#setMaxZoom caps maxZoom at 20

[jlaxson]

It is possible to initialize a map using options that specify an arbitrary maxZoom (Transform's default is 22). However, Map#setMaxZoom will refuse to later set any value above 20.

setMaxZoom with this behavior was added by #2235 and #2243, but I can't find anywhere in the issue history or commit logs where it is explicitly said that this was intentional or necessary.

I have some high resolution rasters whose tiles reach their native resolution at zooms 22-24.

mapbox-gl-js version: 0.28.0

Steps to Trigger Behavior

http://jsbin.com/sozesekomi/edit?html,js,output

1. Initialize map with maxZoom greater than 20. This works and map can zoom way in.
2. Call setMaxZoom with another value greater than 20

Expected Behavior

Max zoom is adjusted to given value, and current zoom is clamped as necessary.

Actual Behavior

Error thrown that maxZoom must be between minZoom and 20.

[1ec5]

Relatedly, mapbox/mapbox-gl-native#7155 tracks increasing the maximum zoom level beyond 21 in the native SDKs.