Fix mgheatmap,gs.order param functionality

[lianos]

The gs.order parameter looks to be broken, probably due to the powerful ComplexHeatmap refactoring that landed in Bioc3.9 (ComplexHeatmap v2)

[lianos]

This actually works when cluster_rows = FALSE, which ... makes sense, but I could have sworn we could keep the intra-split row clustering while reordering the groups in split before v2