### Godot version

v4.2.dev4.official [549fcce5f]

### System information

Ubuntu 20.04 LTS

### Issue description

See title.

### Steps to reproduce

1. Create a new project
2. Create a csv file that includes the following
```
key,ar
key,placeholder
```
3. Add the generated `.translation` file to Project -> Project Settings... -> Localization
4. In Project -> Project Settings... -> Internationalization -> Locale, set `Test` to `ar`
5. Add a `LineEdit` node and type `-=[]{}`
6. Run the project, and notice that the text is on the right side, but the symbols are incorrectly in LTR (`-=[]{}`).  Correct output is `{}[]=-`
7. Back in the editor, add a single Arabic letter (any will do), and notice that `LineEdit` immediately (and correctly) flips the symbols, and the newly-added Arabic letter, to RTL.

**Notes**
- Identical behavior is seen with `TextEdit`.
- The purpose of steps 2-4 are to simulate an Arabic environment when the project is run, despite `OS.get_locale() == "en"` (or your system's current language).

### Minimal reproduction project

[rtlsymbols.zip](https://github.com/godotengine/godot/files/12525509/rtlsymbols.zip)
RID f;
	int fs = p_sd->spans[p_span].font_size;
	if (p_fb_index >= 0 && p_fb_index < p_fonts.size()) {
		
		f = p_fonts[p_fb_index];
	} else if (OS::get_singleton()->has_feature("system_fonts") && p_fonts.size() > 0 && ((p_fb_index == p_fonts.size()) || (p_fb_index > p_fonts.size() && p_start != p_prev_start))) {
		
		RID fdef = p_fonts[0];
		if (_font_is_allow_system_fallback(fdef)) {
			_update_chars(p_sd);
			int64_t next = p_end;
			for (const int32_t &E : p_sd->chars) {
				if (E > p_start) {
					next = E;
					
				}
			}
			String text = p_sd->text.substr(p_start, next - p_start);