Add Object support for String.format

[4d49]

This adds Object as argument for formatting strings.

Example:

extends Node2D


func _ready() -> void:
	# Prints: Position: (0, 0); Rotation: 0
	print("Position: {position}; Rotation: {rotation}".format(self))
	
	# Prints: Visible: true; Scale: (1, 1)
	print("Visible: {visible}; Scale: {scale}".format(self))

Closes godotengine/godot-proposals#5434

[akien-mga]

Looks good! Could you squash the commits? See PR workflow for instructions.

[4d49]

Looks good! Could you squash the commits? See PR workflow for instructions.

Done.

[YuriSizov]

Seems like we missed this one, sorry. Needs a rebase, and I guess it can then be merged for 4.1.

[Repiteo]

Thanks!