Added

• Add legend.xref and legend.yref to enable container-referenced positioning of legends [#6589], with thanks to Gamma Technologies for sponsoring the related development.
• Add colorbar.xref and colorbar.yref to enable container-referenced positioning of colorbars [#6593], with thanks to Gamma Technologies for sponsoring the related development.

Changed

• Improve heatmap rendering performance when zsmooth is set to false [#6574], with thanks to @lvlte for the contribution!