### 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
case ENUM:
		case EXTENDS:
		case FOR:
		case FUNC:
		case IF:
		case IN:
		case IS:
		case MATCH:
		case NAMESPACE:
		case NOT:
		case OR:
		case PASS:
		case PRELOAD:
		case RETURN:
		case SELF:
		case SIGNAL:
		case STATIC:
		case SUPER:
		case TRAIT:
		case UNDERSCORE:
		case VAR:
		case VOID:
		case WHILE:
		case YIELD:
			return true;
		default:
			return false;
	}
}
String GDScriptTokenizer::get_token_name(Token::Type p_token_type) {