Use switch consistently in _notification (scene folder)

[akien-mga]

Unifies the code style in _notification methods by using switch statements consistently, with the following opinionated style (which mostly matches our current "best practice", at least it's what recently added code tends to use):

void MyClass::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_ENTER_TREE:
		case NOTIFICATION_MOVED_IN_PARENT: {
			// Do stuff.
		} break;

		case NOTIFICATION_EXIT_TREE: {
			// Do other stuff.
		} break;

		case NOTIFICATION_FOCUS_ENTER: {
			// Do custom stuff for focus enter.
			[[fallthrough]];
		}
		case NOTIFICATION_FOCUS_EXIT: {
			// Do common stuff for any focus change.
		} break;
}

I.e.:

• Always use brackets for case blocks
• Always use break; after the closing bracket
• Keep a separation line between cases, unless they're a fallthrough (instead of using a weird empty line before } break;)
  • This is not a policy for all switch statements in the codebase, only for _notification ones which tend to be very big. (Can still be used for other switches as needed when more visual separation helps readability.)

---

Reviewing the whole of scene was a pretty tedious 2.5 hours of work, I might solicit contributors help to port the rest of the codebase if we agree about those changes.

This is best reviewed with whitespace changes hidden (add ?w=1 to PR files view URL): https://github.com/godotengine/godot/pull/58151/files?w=1

[akien-mga]

Note about [[fallthrough]]: IMO it would look better if it could be put in the place of break;, like this:

		case NOTIFICATION_FOCUS_ENTER: {
			// Do custom stuff for focus enter.
		} [[fallthrough]];
		case NOTIFICATION_FOCUS_EXIT: {
			// Do common stuff for any focus change.
		} break;

But IIRC this didn't work at least for some compilers as the attribute is expected to qualify a null statement, which the { } code block isn't.
It might work with:

		case NOTIFICATION_FOCUS_ENTER: {
			// Do custom stuff for focus enter.
		}; [[fallthrough]];
		case NOTIFICATION_FOCUS_EXIT: {
			// Do common stuff for any focus change.
		} break;

(added semicolon)
or:

		case NOTIFICATION_FOCUS_ENTER: {
			// Do custom stuff for focus enter.
		}
		[[fallthrough]];
		case NOTIFICATION_FOCUS_EXIT: {
			// Do common stuff for any focus change.
		} break;

But I'll experiment with those in a separate PR.

---

Edit:

Well } [[fallthrough]]; seems to work fine with latest GCC and Clang at least, tested on this use case with:

class SomeClass {
public:
	enum SomeEnum {
		A,
		B,
	};

	int handle_a(SomeEnum a) {
		int b = 0;
		switch (a) {
			case A: {
				b = 42;
			} [[fallthrough]];
			case B:
				b = 12;
				break;
			default:
				b = 128;
				break;
		}
		return b;
	}
};

int main() {
	SomeClass c;
	return c.handle_a(SomeClass::A);
}

I'll change these in a follow-up PR throughout the codebase.

---

Edit 2: Now I remember why we can't use this code style. clang-format messes it up:

diff --git a/core/io/http_client_tcp.cpp b/core/io/http_client_tcp.cpp
index 23381257e5..c5550a29df 100644
--- a/core/io/http_client_tcp.cpp
+++ b/core/io/http_client_tcp.cpp
@@ -132,7 +132,8 @@ static bool _check_request_url(HTTPClientTCP::Method p_method, const String &p_u
 			if (p_url == "*") {
 				return true;
 			}
-		} [[fallthrough]];
+		}
+			[[fallthrough]];
 		default:
 			// Absolute path or absolute URL.
 			return p_url.begins_with("/") || p_url.begins_with("http://") || p_url.begins_with("https://");

[YuriSizov]

Long overdue!