### 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
multiline_mode = p_state;
}
void GDScriptTokenizer::push_expression_indented_block() {
	indent_stack_stack.push_back(indent_stack);
}
void GDScriptTokenizer::pop_expression_indented_block() {
	ERR_FAIL_COND(indent_stack_stack.size() == 0);
	indent_stack = indent_stack_stack.back()->get();
	indent_stack_stack.pop_back();
}
int GDScriptTokenizer::get_cursor_line() const {
	return cursor_line;
}
int GDScriptTokenizer::get_cursor_column() const {
	return cursor_column;
}
bool GDScriptTokenizer::is_past_cursor() const {
	if (line < cursor_line) {
		return false;
	}
	if (line > cursor_line) {
		return true;
	}
	if (column < cursor_column) {
		return false;
	}
	return true;
}
char32_t GDScriptTokenizer::_advance() {