### 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 (!skip) {
								draw_glyph(ellipsis_glyphs[gl_idx], ci, font_color, ofs);
							}
							processed_glyphs++;
							ofs.x += ellipsis_glyphs[gl_idx].advance;
						}
					}
				}
				
				for (int j = 0; j < gl_size; j++) {
					
					if (trim_pos >= 0) {
						if (rtl) {
							if (j < trim_pos) {
								continue;
							}
						} else {
							if (j >= trim_pos) {
								break;
							}
						}
					}
					for (int k = 0; k < glyphs[j].repeat; k++) {
						bool skip = (trim_chars && glyphs[j].end > visible_chars) || (trim_glyphs_ltr && (processed_glyphs >= visible_glyphs)) || (trim_glyphs_rtl && (processed_glyphs < total_glyphs - visible_glyphs));
						
						if (!skip) {
							draw_glyph(glyphs[j], ci, font_color, ofs);
						}
						processed_glyphs++;