### 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
push_error(vformat(R"(Identifier "%s" is visually similar to the GDScript keyword "%s" and thus not allowed.)", name, keyword_list[confusable]));
		}
	}
#endif 
	return id;
#undef KEYWORD_GROUP_CASE
#undef KEYWORD
}
#undef MAX_KEYWORD_LENGTH
#undef MIN_KEYWORD_LENGTH
#undef KEYWORDS
void GDScriptTokenizer::newline(bool p_make_token) {
	
	if (p_make_token && !pending_newline && !line_continuation) {
		Token newline(Token::NEWLINE);
		newline.start_line = line;
		newline.end_line = line;
		newline.start_column = column - 1;
		newline.end_column = column;
		newline.leftmost_column = newline.start_column;
		newline.rightmost_column = newline.end_column;
		pending_newline = true;
		last_newline = newline;
	}
	
	line++;
	column = 1;
	leftmost_column = 1;
}
GDScriptTokenizer::Token GDScriptTokenizer::number() {