### 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)

PackedStringArray warnings = Control::get_configuration_warnings();
	
	Ref<Font> font;
	if (settings.is_valid()) {
		font = settings->get_font();
	}
	if (font.is_null()) {
		font = theme_cache.font;
	}
	if (font.is_valid()) {
		if (dirty || font_dirty || lines_dirty) {
			const_cast<Label *>(this)->_shape();
		}
		const Glyph *glyph = TS->shaped_text_get_glyphs(text_rid);
		int64_t glyph_count = TS->shaped_text_get_glyph_count(text_rid);
		for (int64_t i = 0; i < glyph_count; i++) {
			if (glyph[i].font_rid == RID()) {
				warnings.push_back(RTR("The current font does not support rendering one or more characters used in this Label's text."));
				break;
			}
		}
	}
	return warnings;
}
void Label::_notification(int p_what) {