Improve runtime resources (timelines and characters created through code)

[Jowan-Spooner]

This makes both DialogicTimeline and DialogicCharacter extend DialogicIdentifiableResource which basically adds a get_identifier and set_identifier method. If an identifier is set at runtime for a non-saved resource, the resource is registered to the directories directly (without a path) allowing for the use of those resources in timelines from then on.

        var characterA := DialogicCharacter.new()
	characterA.display_name = "Code Character"
	characterA.color = Color.WEB_PURPLE
	characterA.set_identifier("CodeCharacter")

	var timelineA := DialogicTimeline.new()
	timelineA.from_text(
	"""
		CodeCharacter: Timeline A!!!
		jump CodeTimelineB/
		label Section2
		CodeCharacter: About to end timeline A.
	""")
	timelineA.set_identifier("CodeTimelineA")

	var timelineB := DialogicTimeline.new()
	timelineB.from_text(
	"""
		Timeline B!!!
		jump CodeTimelineA/Section2
	"""
	)
	timelineB.set_identifier("CodeTimelineB")

	Dialogic.start(timelineA)

• fixes jump not working on timeline created by code #2492
• fixes Create a character in gdscript without requiring saving a local file #2491

This also once again allows using "invalid" character names in timelines (a new character resource will be created on the spot) and will now even interpret the portrait as a color for those, which allows to have one-off characters say something. However the portrait picker is not shown in the visual editor for those characters for now so this is kinda a text-editor exclusive rn.

"Random person" (webpurple): Wait who's that?
"Other person" (darkblue): I think that's the new guy.

Also fixes a bug with dictionaries as export overrides for custom portraits.

[shazzner]

Great work!