[3.x] Add Image::fill_rect method

[kleonc]

3.x version of #52456.

[AaronRecord]

Did some basic profiling for fun using the CI builds, depending on the situation the new fill method is about ~7-11 times faster than the current 3.x one.

script used

extends TextureRect


var image := Image.new()


func _ready() -> void:
	image.create(1000, 1000, false, Image.FORMAT_RGBA8)


func _process(delta: float) -> void:
	var start := OS.get_ticks_msec()
	for i in 1000:
		image.fill(Color(rand_range(0, 1), rand_range(0, 1), rand_range(0, 1)))
	print(OS.get_ticks_msec() - start)

[akien-mga]

Could use a rebase to be safe.

[akien-mga]

Thanks!