### 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)
const String lang = (p_language.is_empty()) ? TranslationServer::get_singleton()->get_tool_locale() : p_language;
	// Convert to UTF-16.
	Char16String utf16 = p_string.utf16();
	PackedInt32Array ret;
	UErrorCode err = U_ZERO_ERROR;
	UBreakIterator *bi = ubrk_open(UBRK_CHARACTER, lang.ascii().get_data(), (co_data(), utf16.length(), &err);
	if (U_SUCCESS(err)) {
		while (ubrk_next(bi) != UBRK_DONE) {
			int pos = _convert_pos(p_string, utf16, ubrk_current(bi));
			ret.push_back(pos);
		}
		ubrk_close(bi);
	} else {
		for (int i = 0; i <= p_string.size(); i++) {
			ret.push_back(i);
		}
	}
	return ret;
}
bool TextServerAdvanced::_is_valid_identifier(const String &p_string) const {
#ifndef ICU_STATIC_DATA
	if (!icu_data_loaded) {
		WARN_PRINT_ONCE("ICU data is not loaded, Unicode security and spoofing detection disabled.");
		return TextServer::is_valid_identifier(p_string);
	}
#endif
	enum UAX31SequenceStatus {
		SEQ_NOT_STARTED,