### 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
result += ch;
			_advance();
			if (ch == '\n') {
				newline(false);
			}
		}
	}
	if (prev != 0) {
		Token error = make_error("Invalid UTF-16 sequence in string, unpaired lead surrogate");
		error.start_column = prev_pos;
		error.leftmost_column = error.start_column;
		push_error(error);
		prev = 0;
	}
	
	Variant string;
	switch (type) {
		case STRING_NAME:
			string = StringName(result);
			break;
		case STRING_NODEPATH:
			string = NodePath(result);
			break;
		case STRING_REGULAR:
			string = result;
			break;
	}
	return make_literal(string);
}
void GDScriptTokenizer::check_indent() {