### 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)

ofs.x = style->get_offset().x;
						}
						break;
					case HORIZONTAL_ALIGNMENT_LEFT: {
						if (rtl_layout) {
							ofs.x = int(size.width - style->get_margin(SIDE_RIGHT) - line_size.width);
						} else {
							ofs.x = style->get_offset().x;
						}
					} break;
					case HORIZONTAL_ALIGNMENT_CENTER: {
						ofs.x = int(size.width - line_size.width) / 2;
					} break;
					case HORIZONTAL_ALIGNMENT_RIGHT: {
						if (rtl_layout) {
							ofs.x = style->get_offset().x;
						} else {
							ofs.x = int(size.width - style->get_margin(SIDE_RIGHT) - line_size.width);
						}
					} break;
				}
				const Glyph *glyphs = TS->shaped_text_get_glyphs(lines_rid[i]);
				int gl_size = TS->shaped_text_get_glyph_count(lines_rid[i]);
				int ellipsis_pos = TS->shaped_text_get_ellipsis_pos(lines_rid[i]);
				int trim_pos = TS->shaped_text_get_trim_pos(lines_rid[i]);
				const Glyph *ellipsis_glyphs = TS->shaped_text_get_ellipsis_glyphs(lines_rid[i]);
				int ellipsis_gl_size = TS->shaped_text_get_ellipsis_glyph_count(lines_rid[i]);
				
				int processed_glyphs_ol = processed_glyphs;
				if ((outline_size > 0 && font_outline_color.a != 0) || (font_shadow_color.a != 0)) {