[SUGGESTION] allow _get_property_list() to contribute to auto complete

[xDGameStudios]

OS/device including version:
N/A

Issue description:
Normally when working with tool you may want to expose custom variables to the to the inspector. For example allow _get_property_list to retrieve entries in a Dictionary... it would be nice if the suggestion for those properties should up in the autocomplete, if the dictionary is made const. if it is a constant and we are working with tool scripts I guess it would be doable? what do you think?

tool
extends Object
class_name MyObject

const dict = { "size": 1, "width": 2 }

func _get_property_list():
     var ret = []
     for a_name in dict:
          ret.append({"name": a_name, "type": TYPE_INT, "usage": PROPERTY_USAGE_DEFAULT})

this would make it possible to:

var a = MyObject.new()
a.size # this would appear in the autocomplete
a.width # this would appear in the autocomplete

What do you think? Worth it? Doable?

[mrcdk]

Duplicate of #25097

[xDGameStudios]

Sorry for the dup @mrcdk.