### 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
return make_token(Token::PIPE_EQUAL);
			} else {
				return make_token(Token::PIPE);
			}
		
		case '=':
			if (_peek() == '=') {
				return check_vcs_marker('=', Token::EQUAL_EQUAL);
			} else {
				return make_token(Token::EQUAL);
			}
		case '<':
			if (_peek() == '=') {
				_advance();
				return make_token(Token::LESS_EQUAL);
			} else if (_peek() == '<') {
				if (_peek(1) == '=') {
					_advance();
					_advance(); 
					return make_token(Token::LESS_LESS_EQUAL);
				} else {
					return check_vcs_marker('<', Token::LESS_LESS);
				}
			} else {
				return make_token(Token::LESS);
			}
		case '>':
			if (_peek() == '=') {
				_advance();
				return make_token(Token::GREATER_EQUAL);