LibGUI: Rewrite layout system in terms of min and max sizes

This patch removes size policies and preferred sizes, and replaces them
with min-size and max-size for each widget.

Box layout now works in 3 passes:

    1) Set all items (widgets/spacers) to their min-size
    2) Distribute remaining space evenly, respecting max-size
    3) Place widgets one after the other, adding spacing in between

I've also added convenience helpers for setting a fixed size (which is
the same as setting min-size and max-size to the same value.)

This significantly reduces the verbosity of widget layout and makes GML
a bit more pleasant to write, too. :^)

1 files changed, 1 insertions, 2 deletions

diff --git a/Demos/HelloWorld/main.cpp b/Demos/HelloWorld/main.cpp
index 7f2b70fc54..da30d56554 100644
--- a/Demos/HelloWorld/main.cpp
+++ b/Demos/HelloWorld/main.cpp
@@ -68,8 +68,7 @@ int main(int argc, char** argv)
 
     auto& button = main_widget.add<GUI::Button>();
     button.set_text("Good-bye");
-    button.set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fixed);
-    button.set_preferred_size(0, 20);
+    button.set_fixed_height(20);
     button.on_click = [&](auto) {
         app->quit();
     };