### 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
if (indent_level() == 0) {
				push_error("Tokenizer bug: trying to dedent without previous indent.");
				return;
			}
			while (indent_level() > 0 && indent_stack.back()->get() > indent_count) {
				indent_stack.pop_back();
				pending_indents--;
			}
			if ((indent_level() > 0 && indent_stack.back()->get() != indent_count) || (indent_level() == 0 && indent_count != 0)) {
				
				Token error = make_error("Unindent doesn't match the previous indentation level.");
				error.start_line = line;
				error.start_column = 1;
				error.leftmost_column = 1;
				error.end_column = column + 1;
				error.rightmost_column = column + 1;
				push_error(error);
				
				indent_stack.push_back(indent_count);
			}
		}
		break; 
	}
}
String GDScriptTokenizer::_get_indent_char_name(char32_t ch) {
	ERR_FAIL_COND_V(ch != ' ' && ch != '\t', String(&ch, 1).c_escape());
	return ch == ' ' ? "space" : "tab";
}
void GDScriptTokenizer::_skip_whitespace() {