Issue #2760659 by lauriii, yogeshmpawar, vmachado, anya_m, alexpott, Fabianx, joelpittet, xjm: Allow the use of callbacks instead of global functions in preprocess function callbacks

Issue #2850010 by anish.a, joachim, vmachado, tameeshb: Remove documentation references to deprecated function menu_local_tasks()

This reverts commit e72c97b9.