### Godot version

4.0

### System information

All OS/Hardware

### Issue description

Not sure if it's a bug / inconsistency or a willingness 😄

When writing numbers in GDScript, we can use `_` character to make number more readable for a human. Rules for this character differ depending on where it is used : before or in decimal part, making its usage inconsistent. 
- When use before decimal part, only an underscore can not follow another undersocre
- In decimal part, multiple underscores can be write without any complaint of tokenizer



### Steps to reproduce

Here is test functions to illustrate

```gdscript
func test_number_allowed_without_error() -> void:
    var a:int = 1_2_3_4_5_6
    var b:int = 123_456
    var c:int = 1.2_3_4_5_6
    var d:int = 1.2_____3_____4____5_____6
    var e:int = 1._2_3_4_5
    var f:int = 1.________23456

func test_number_not_allowed() -> void:
    var a:int = 1__2
    var b:int = 1__2.1__2
    var c:int = _1.23456
```

With a screen to show editor syntax errors

![image](https://user-images.githubusercontent.com/121614863/220851058-38439a3f-3ba8-40fa-9556-a0faf045c943.png)

### Minimal reproduction project

N/A
if (paren_stack.is_empty()) {
		return make_error(vformat("Closing \"%c\" doesn't have an opening counterpart.", p_paren));
	}
	Token error = make_error(vformat("Closing \"%c\" doesn't match the opening \"%c\".", p_paren, paren_stack.back()->get()));
	paren_stack.pop_back(); 
	return error;
}
GDScriptTokenizer::Token GDScriptTokenizer::check_vcs_marker(char32_t p_test, Token::Type p_double_type) {
	const char32_t *next = _current + 1;
	int chars = 2; 
	
	while (*next == p_test) {
		chars++;
		next++;
	}
	if (chars >= 7) {
		
		while (chars > 1) {
			
			_advance();
			chars--;
		}
		return make_token(Token::VCS_CONFLICT_MARKER);
	} else {
		
		_advance();
		return make_token(p_double_type);
	}
}
GDScriptTokenizer::Token GDScriptTokenizer::annotation() {