Setting a text that contains emojis to a textedit is slow

### Tested versions

- v4.2.stable.mono.official [46dc27791]
- v4.2.1.stable.mono.official [b09f793f5]

### System information

Godot v4.2.stable.mono - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4080 (NVIDIA; 31.0.15.5123) - AMD Ryzen 9 7950X3D 16-Core Processor (32 Threads)

### Issue description

I have a `TextEdit` node that I pre-fill with some text that contains a range of emojis. In my example I set about 300 lines of text each line containing an emoji. Setting this text of 300 lines with emojis to the `text` property of the `TextEdit` takes about 16-18ms on my machine. If I remove the emojis from the text, the same operation only takes about 2-3ms on my machine.

### Steps to reproduce

In the example project I have this script which will produce a text at the start and then try to set it every frame:

```gdscript
extends Control

@onready var text_edit = $TextEdit

var text:String

func _ready():
text = make_300_lines()

func _process(delta):
text_edit.text = text

func make_300_lines():
var emojis = ["🔴", "🟢", "⚡", "↪️"]
var result:String = ""
for i in 300:
# use the following line to get a text without emojis
# result += " this is a line " + "[c]" + "\n"

# this will produce a text with emojis
# comment it to use the other line
result += " this is a line " + emojis.pick_random() + "\n"

return result

```

You can use the alternative line to produce a text without emojis. Profile each variant to see the difference in performance.

### Minimal reproduction project (MRP)

[emoji_reproducer.zip](https://github.com/godotengine/godot/files/14396079/emoji_reproducer.zip)

Start with the provided emoji_reproducer.zip and run the TextEdit script that assigns 300 lines every frame. Profile the emoji and non-emoji variants to identify where the extra time is spent. Done means the emoji case is measurably closer to the non-emoji case without breaking TextEdit behavior.

Written by the indexing model from the issue text.