### 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
_advance();
			newline(false);
			continue;
		}
		if (_peek() == '#') {
			
#ifdef TOOLS_ENABLED
			String comment;
			while (_peek() != '\n' && !_is_at_end()) {
				comment += _advance();
			}
			comments[line] = CommentData(comment, true);
#else
			while (_peek() != '\n' && !_is_at_end()) {
				_advance();
			}
#endif 
			if (_is_at_end()) {
				
				pending_indents -= indent_level();
				indent_stack.clear();
				return;
			}
			_advance(); 
			newline(false);
			continue;
		}
		if (line_continuation || multiline_mode) {