Rationalize Node removals and deletions

[RandomShaper]

• Regarding preservation of owner, free() and remove_child() now behave the same: owner is kept during tree_exiting signal and null during tree_exited.
• tree_exited is emitted in the same order as tree_exiting.
• Superfluous code to handle cancelation of ownership is removed.

Tested with the following composite scene (full project, where exact ownerships can be checked: Minimal.zip:

Main's code:

extends Node2D

func _ready():
	var se1f = self
	$A.connect(\"tree_exiting\", Callable(se1f, \"exiting\"), [$A])
	$A.connect(\"tree_exited\", Callable(se1f, \"exited\"), [$A])
	$A/Node.connect(\"tree_exiting\", Callable(se1f, \"exiting\"), [$A/Node])
	$A/Node.connect(\"tree_exited\", Callable(se1f, \"exited\"), [$A/Node])
	$A/Node/B.connect(\"tree_exiting\", Callable(se1f, \"exiting\"), [$A/Node/B])
	$A/Node/B.connect(\"tree_exited\", Callable(se1f, \"exited\"), [$A/Node/B])
	$A/Node/B/B2.connect(\"tree_exiting\", Callable(se1f, \"exiting\"), [$A/Node/B/B2])
	$A/Node/B/B2.connect(\"tree_exited\", Callable(se1f, \"exited\"), [$A/Node/B/B2])
	$A/Node/B/C.connect(\"tree_exiting\", Callable(se1f, \"exiting\"), [$A/Node/B/C])
	$A/Node/B/C.connect(\"tree_exited\", Callable(se1f, \"exited\"), [$A/Node/B/C])
	# Uncomment either, never both
	#remove_child($A)
	$A.free()

func exiting(node):
	prints(\"exiting\", node.name, node.owner) #prints node; before it was null

func exited(node):
	prints(\"exited\", node.name, node.owner) #prints null

Results with current code (before this PR)

With $A.free():

exiting C Node2D:[Node2D:29192356323]
exiting B2 B:[Node2D:29242687969]
exiting B Node2D:[Node2D:29192356323]
exiting Node [Object:null]
exiting A [Object:null]
exited B2 B:[Node2D:29242687969]
exited C [Object:null]
exited B [Object:null]
exited Node [Object:null]
exited A [Object:null]

With remove_child($A):

exiting C Node2D:[Node2D:29192356324]
exiting B2 B:[Node2D:29242687969]
exiting B Node2D:[Node2D:29192356324]
exiting Node A:[Node2D:29209133539]
exiting A Node2D:[Node2D:29192356324]
exited B2 B:[Node2D:29242687969]
exited C [Object:null]
exited B [Object:null]
exited Node A:[Node2D:29209133539]
exited A [Object:null]

Results with this PR

With $A.free() or remove_child($A) (same results in both cases):

# tree_exiting preserves owners
exiting C Node2D:[Node2D:29192356600]
exiting B2 B:[Node2D:29242688246]
exiting B Node2D:[Node2D:29192356600]
exiting Node A:[Node2D:29209133817]
exiting A Node2D:[Node2D:29192356600]

# - Owners are already cleared by tree_exited
# - tree_exited comes in tree reverse order, like tree_exiting
exited C [Object:null]
exited B2 [Object:null]
exited B [Object:null]
exited Node [Object:null]
exited A [Object:null]

---

Supersedes #39835.
Fixes #22840.

NOTE: A non compat breaking subset of this PR for 3.x has been submitted separately: #55514.

[akien-mga]

Thanks!