Fix starting order for RollbackSynchronizer

[TheYellowArchitect]

Solves #260 and #268 by fixing input initialization.

Also gets rid of the await 1 frame hack for 2 seperate classes (BrawlerController.gd/player.gd) in order to await for input authority to be set before process_authority, so this awaiting a frame logic is moved to RollbackSynchronizer since in most games, input authority is set in _ready or something similar.

May also solve the reported problem of the first 2 ticks, having NPCs spinning. Haven't seen it in a project of mine, but it may solve it because this PR addresses the first _earliest_input being set properly

[TheYellowArchitect]

This variable ultimately ended up being unused, but its useful to keep so as to know when an avatar joined/started.

[TheYellowArchitect]

After await, it is basically guaranteed the input authority is set, so process_authority can be safely invoked

[TheYellowArchitect]

Debug comment, to confirm #260 is fixed. Place this message on main branch, and you will see it goes from 0 to current. I will remove this message once this PR is reviewed/approved

[TheYellowArchitect]

And that's what I did :P

[TheYellowArchitect]

EDIT: The below is arguments against and for, the await 1 frame logic, ultimately ending in for keeping things as the code in this PR is.

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Btw the "await 1 frame" logic could be skipped entirely. It is only useful if the Input authority is set in the same PackedScene as RollbackSynchronizer. The tree order in Godot is top to bottom. So if the input authority is set in _ready, then that Input node must be above RollbackSynchronizer, so Input's _ready fires before RollbackSynchronizer's.

At forest-brawl, the input authority isn't set at _ready of root brawler or at _ready of Input, but outside, at the spawner:

func _spawn(id: int) -> BrawlerController:
	var avatar = player_scene.instantiate() as BrawlerController
	avatars[id] = avatar
	avatar.name += " #%d" % id
	avatar.player_id = id
	spawn_root.add_child(avatar)
	
	# Avatar is always owned by server
	avatar.set_multiplayer_authority(1)

	print("Spawned avatar %s at %s" % [avatar.name, multiplayer.get_unique_id()])
	
	# Avatar's input object is owned by player
	var input = avatar.find_child("Input")
	if input != null:
		input.set_multiplayer_authority(id)
		print("Set input(%s) ownership to %s" % [input.name, id])
	

So as it is, without the await 1 frame, all _ready trigger, and then input authority is set -> which ofc bugs.
Ideally, input authority would be set inside _ready of Input node. I can expand this PR for this, and to remove the await 1 frame, but that would make setting input authority outside the PackedScene impossible, so I suggest keeping this PR as is.