### 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)

} break;
					case VERTICAL_ALIGNMENT_CENTER: {
						vbegin = (size.y - (total_h - line_spacing)) / 2;
						vsep = 0;
					} break;
					case VERTICAL_ALIGNMENT_BOTTOM: {
						vbegin = size.y - (total_h - line_spacing);
						vsep = 0;
					} break;
					case VERTICAL_ALIGNMENT_FILL: {
						vbegin = 0;
						if (lines_visible > 1) {
							vsep = (size.y - (total_h - line_spacing)) / (lines_visible - 1);
						} else {
							vsep = 0;
						}
					} break;
				}
			}
			Vector2 ofs;
			ofs.y = style->get_offset().y + vbegin;
			for (int i = lines_skipped; i < last_line; i++) {
				Size2 line_size = TS->shaped_text_get_size(lines_rid[i]);
				ofs.x = 0;
				ofs.y += TS->shaped_text_get_ascent(lines_rid[i]);
				switch (horizontal_alignment) {
					case HORIZONTAL_ALIGNMENT_FILL:
						if (rtl && autowrap_mode != TextServer::AUTOWRAP_OFF) {
							ofs.x = int(size.width - style->get_margin(SIDE_RIGHT) - line_size.width);
						} else {