heatmapgl does not coerce its own attributes

[archmoj]

The heatmapgl trace needs its own default function.
Right now it uses heatmap default and attributes.
As a result attributes e.g. zsmooth, xgap, connectgaps, hoverongaps, and more get into gd._fullData.

[archmoj]

This is a bug we need to fix before #4924. Whereas the default smoothing of heatmapgl is similar to fast, zsmooth is actually set to false!