### Godot version

4.0.3 stable

### System information

Windows 10, i5 8600, RTX3060, 64 GB ram

### Issue description

In Godot 4, labels with lots of text cause scenes to load extremely slowly, both in the editor and in-game.

I measured a few game starts with different amounts of text in a label:

Text length | Game start time
-- | --
11323 | 2.33
22693 | 7.93
34064 | 19.69
45431 | 40.59

In Godot 3, the startup times for all test lengths was almost instantaneous.

The text I used was multiple copies of the license agreement for Google's [Roboto](https://fonts.google.com/specimen/Roboto) font. A "credits" page on a game could easily get well above this length.
Looking at a scatter plot with a best fit, it's pretty clearly increasing at around n^2:

![image](https://github.com/godotengine/godot/assets/8082633/6e2a9c41-f3fb-429d-acd3-288c24c6b744)

Results are the same whether I'm using the built-in font or a custom font, and results are similar across all renderers. Settings like text wrapping don't seem to affect it either.

### Steps to reproduce

Create a scene, add a label to that scene, and fill the label with a large amount of text. Try to launch the game and load that scene.

### Minimal reproduction project

[Godot3LargeLabel.zip](https://github.com/godotengine/godot/files/11521494/Godot3LargeLabel.zip)
[Godot4LargeLabel.zip](https://github.com/godotengine/godot/files/11521495/Godot4LargeLabel.zip)

if (dirty || font_dirty || lines_dirty) {
		const_cast<Label *>(this)->_shape();
	}
	Size2 min_size = minsize;
	const Ref<Font> &font = (settings.is_valid() && settings->get_font().is_valid()) ? settings->get_font() : theme_cache.font;
	int font_size = settings.is_valid() ? settings->get_font_size() : theme_cache.font_size;
	min_size.height = MAX(min_size.height, font->get_height(font_size) + font->get_spacing(TextServer::SPACING_TOP) + font->get_spacing(TextServer::SPACING_BOTTOM));
	Size2 min_style = theme_cache.normal_style->get_minimum_size();
	if (autowrap_mode != TextServer::AUTOWRAP_OFF) {
		return Size2(1, (clip || overrun_behavior != TextServer::OVERRUN_NO_TRIMMING) ? 1 : min_size.height) + min_style;
	} else {
		if (clip || overrun_behavior != TextServer::OVERRUN_NO_TRIMMING) {
			min_size.width = 1;
		}
		return min_size + min_style;
	}
}
int Label::get_line_count() const {