Support grid descriptors

[joaomoreno]

This lays the foundation for #50674.

The createSerializedGrid function lets you convert a grid descriptor (same interface as the argument of the layoutEditorGroups command) and that will return a SerializedGrid instance.

You can then throw the entire grid away and use that instance to create a new SerializedGrid, using a special deserializer which reuses old editor groups from an array, as discussed.

@bpasero I'll leave the rest up to you!

[bpasero]

@joaomoreno thanks will have a look