[3.x] Enable zooming in graph_edit with `Ctrl + scrollwheel` + relevant cherry-picks#47173

Merged

akien-mga merged 6 commits intogodotengine:3.xfrom AaronRecord:graphedit-zoom-cherrypicks

Apr 29, 2021

+89-106

Commits on Apr 6, 2021

Make scrollwheel zoom based on mouse position, cherry-picked for 3.x
AaronRecord
committed

Commits on Apr 26, 2021

Initialize some graphedit values in the header
AaronRecord
committed