### 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)

ClassDB::bind_method(D_METHOD("get_tab_stops"), &Label::get_tab_stops);
	ClassDB::bind_method(D_METHOD("set_text_overrun_behavior", "overrun_behavior"), &Label::set_text_overrun_behavior);
	ClassDB::bind_method(D_METHOD("get_text_overrun_behavior"), &Label::get_text_overrun_behavior);
	ClassDB::bind_method(D_METHOD("set_uppercase", "enable"), &Label::set_uppercase);
	ClassDB::bind_method(D_METHOD("is_uppercase"), &Label::is_uppercase);
	ClassDB::bind_method(D_METHOD("get_line_height", "line"), &Label::get_line_height, DEFVAL(-1));
	ClassDB::bind_method(D_METHOD("get_line_count"), &Label::get_line_count);
	ClassDB::bind_method(D_METHOD("get_visible_line_count"), &Label::get_visible_line_count);
	ClassDB::bind_method(D_METHOD("get_total_character_count"), &Label::get_total_character_count);
	ClassDB::bind_method(D_METHOD("set_visible_characters", "amount"), &Label::set_visible_characters);
	ClassDB::bind_method(D_METHOD("get_visible_characters"), &Label::get_visible_characters);
	ClassDB::bind_method(D_METHOD("get_visible_characters_behavior"), &Label::get_visible_characters_behavior);
	ClassDB::bind_method(D_METHOD("set_visible_characters_behavior", "behavior"), &Label::set_visible_characters_behavior);
	ClassDB::bind_method(D_METHOD("set_visible_ratio", "ratio"), &Label::set_visible_ratio);
	ClassDB::bind_method(D_METHOD("get_visible_ratio"), &Label::get_visible_ratio);
	ClassDB::bind_method(D_METHOD("set_lines_skipped", "lines_skipped"), &Label::set_lines_skipped);
	ClassDB::bind_method(D_METHOD("get_lines_skipped"), &Label::get_lines_skipped);
	ClassDB::bind_method(D_METHOD("set_max_lines_visible", "lines_visible"), &Label::set_max_lines_visible);
	ClassDB::bind_method(D_METHOD("get_max_lines_visible"), &Label::get_max_lines_visible);
	ClassDB::bind_method(D_METHOD("set_structured_text_bidi_override", "parser"), &Label::set_structured_text_bidi_override);
	ClassDB::bind_method(D_METHOD("get_structured_text_bidi_override"), &Label::get_structured_text_bidi_override);
	ClassDB::bind_method(D_METHOD("set_structured_text_bidi_override_options", "args"), &Label::set_structured_text_bidi_override_options);
	ClassDB::bind_method(D_METHOD("get_structured_text_bidi_override_options"), &Label::get_structured_text_bidi_override_options);
	ADD_PROPERTY(PropertyInfo(Variant::STRING, "text", PROPERTY_HINT_MULTILINE_TEXT), "set_text", "get_text");
	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "label_settings", PROPERTY_HINT_RESOURCE_TYPE, "LabelSettings"), "set_label_settings", "get_label_settings");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "horizontal_alignment", PROPERTY_HINT_ENUM, "Left,Center,Right,Fill"), "set_horizontal_alignment", "get_horizontal_alignment");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "vertical_alignment", PROPERTY_HINT_ENUM, "Top,Center,Bottom,Fill"), "set_vertical_alignment", "get_vertical_alignment");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "autowrap_mode", PROPERTY_HINT_ENUM, "Off,Arbitrary,Word,Word (Smart)"), "set_autowrap_mode", "get_autowrap_mode");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "justification_flags", PROPERTY_HINT_FLAGS, "Kashida Justification:1,Word Justification:2,Justify Only After Last Tab:8,Skip Last Line:32,Skip Last Line With Visible Characters:64,Do Not Skip Single Line:128"), "set_justification_flags", "get_justification_flags");
	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "clip_text"), "set_clip_text", "is_clipping_text");