TextureProgressBar minimal size is prioritized to under -> over -> progress textures

[arkology]

Tested versions

Reproducible since Godot was opensourced.

System information

Not specific to hardware.

Issue description

As title says, TextureProgressBar minimal size is prioritized to under -> over -> progress textures:

Size2 TextureProgressBar::get_minimum_size() const {
	if (nine_patch_stretch) {
		return Size2(stretch_margin[SIDE_LEFT] + stretch_margin[SIDE_RIGHT], stretch_margin[SIDE_TOP] + stretch_margin[SIDE_BOTTOM]);
	} else if (under.is_valid()) {
		return under->get_size();
	} else if (over.is_valid()) {
		return over->get_size();
	} else if (progress.is_valid()) {
		return progress->get_size();
	}

	return Size2(1, 1);
}

So, if someone uses textures with different sizes, they will be surprised that size is not selected as maximum among all "layers".
For example, this is how it looks inside GridContainer:

And this is how it will look if we change minimum size calculation from proprity-based to maximum among all "layers":

To fix it I changed function to the following:

Size2 TextureProgressBar::get_minimum_size() const {
	if (nine_patch_stretch) {
		return Size2(stretch_margin[SIDE_LEFT] + stretch_margin[SIDE_RIGHT], stretch_margin[SIDE_TOP] + stretch_margin[SIDE_BOTTOM]);
	} else {
		Size2 size;
		if (under.is_valid()) {
			size = under->get_size();
		}

		if (progress.is_valid() && progress->get_size() > size) {
			size = progress->get_size();
		}

		if (over.is_valid() && over->get_size() > size) {
			size = over->get_size();
		}
		return size;
	}

	return Size2(1, 1);
}

Of course, it could be solved by enabling nine-patch stretching with zero margins and setting a custom minimum size. And, of course, if no one even reported it before, perhaps no one needs this change.

BUT if changing from priority-based approach to maximum is welcomed, I'll open PR to fix it. I'm sure that "maximum among all layers" is proper behaviour.

Steps to reproduce

Create TextureProgressBar and assign to it textures with different sizes.

Minimal reproduction project (MRP)

New Game Project.zip
Actually this one is my playground to test different TextureProgressBar issues.