Correct superclass constructors in 3to4.

Fixes #70542.

The 3to4 conversion tool was not handling superclass constructors.
We should translate the godot3 syntax:

```gdscript
func _init(a,b,c).(a,b,c):
    pass

func _init(a,b,c):
    super(a,b,c)
```

Originally, the _init conversion was intended to remove `void` return types from _init functions, as this was disallowed due to #50589.
As that was resolved by #53366, I removed that part of the conversion logic. If a void return type is present on a constructor, the converter now leaves it.

Here's a sample diff from my own project:

```diff
@@ -103,10 +105,11 @@ class Real:
 class Text:
        extends Setting

-       var choices: PoolStringArray
-       var value: String setget set_value, get_value
+       var choices: PackedStringArray
+       var value: String : get = get_value, set = set_value

-       func _init(section: String, key: String, default: String, choice_list: Array).(section, key, default) -> void:
+       func _init(section: String, key: String, default: String, choice_list: Array) -> void:
+               super(section, key, default)
                choices = choice_list

        func normalize(val):
@@ -129,9 +132,10 @@ class Text:
 class Boolean:
        extends Setting

-       var value: bool setget set_value, get_value
+       var value: bool : get = get_value, set = set_value

-       func _init(section: String, key: String, default: bool).(section, key, default) -> void:
+       func _init(section: String, key: String, default: bool) -> void:
+               super(section, key, default)
                pass
```

editor/project_converter_3_to_4.cpp

@@ -889,7 +889,10 @@ bool ProjectConverter3To4::test_conversion(RegExContainer &reg_container) {
 	valid = valid && test_conversion_gdscript_builtin("(tween_callback(A,B,[C,D]).foo())", "(tween_callback(Callable(A, B).bind(C,D)).foo())", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
 
 	valid = valid && test_conversion_gdscript_builtin("func _init(", "func _init(", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
-	valid = valid && test_conversion_gdscript_builtin("func _init(p_x:int)->void:", "func _init(p_x:int):", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
+	valid = valid && test_conversion_gdscript_builtin("func _init(a,b,c).(d,e,f):", "func _init(a,b,c):\n\tsuper(d,e,f)", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
+	valid = valid && test_conversion_gdscript_builtin("func _init(a,b,c).(a.b(),c.d()):", "func _init(a,b,c):\n\tsuper(a.b(),c.d())", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
+	valid = valid && test_conversion_gdscript_builtin("func _init(p_x:int)->void:", "func _init(p_x:int)->void:", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
+	valid = valid && test_conversion_gdscript_builtin("func _init(a: int).(d,e,f) -> void:", "func _init(a: int) -> void:\n\tsuper(d,e,f)", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
 	valid = valid && test_conversion_gdscript_builtin("q_PackedDataContainer._iter_init(variable1)", "q_PackedDataContainer._iter_init(variable1)", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
 
 	valid = valid && test_conversion_gdscript_builtin("assert(speed < 20, str(randi()%10))", "assert(speed < 20) #,str(randi()%10))", &ProjectConverter3To4::rename_gdscript_functions, "custom rename", reg_container, false);
@@ -1943,17 +1946,18 @@ void ProjectConverter3To4::process_gdscript_line(String &line, const RegExContai
 			}
 		}
 	}
-	// -- func _init(p_x:int)->void:  -> func _init(p_x:int):    Object # https://github.com/godotengine/godot/issues/50589
-	if (line.contains(" _init(")) {
-		int start = line.find(" _init(");
-		if (line.contains(":")) {
-			int end = line.rfind(":") + 1;
-			if (end > -1) {
-				Vector<String> parts = parse_arguments(line.substr(start, end));
-				line = line.substr(0, start) + " _init(" + connect_arguments(parts, 0) + "):" + line.substr(end + start);
-			}
+	// -- func _init(p_x:int).(p_x):  -> func _init(p_x:int):\n\tsuper(p_x)    Object # https://github.com/godotengine/godot/issues/70542
+	if (line.contains(" _init(") && line.rfind(":") > 0) {
+		//     func _init(p_arg1).(super4, super5, super6)->void:
+		// ^--^indent            ^super_start   super_end^
+		int indent = line.count("\t", 0, line.find("func"));
+		int super_start = line.find(".(");
+		int super_end = line.rfind(")");
+		if (super_start > 0 && super_end > super_start) {
+			line = line.substr(0, super_start) + line.substr(super_end + 1) + "\n" + String("\t").repeat(indent + 1) + "super" + line.substr(super_start + 1, super_end - super_start);
 		}
 	}
+
 	//  assert(speed < 20, str(randi()%10))  ->  assert(speed < 20) #,str(randi()%10))    GDScript - GDScript bug constant message
 	if (line.contains("assert(")) {
 		int start = line.find("assert(");