add(sizing): grow configuration

Currently the 'grid' and 'mixed' examples are not working yet.

examples/styles/text.zig

@@ -114,10 +114,7 @@ pub fn main() !void {
     }, text_styles.element());
     defer box.deinit();
 
-    var scrollable: App.Scrollable = .init(box, .{
-        .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
-        .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
-    }); // ensure enough rows and/or columns to render all text styles -> scrollable otherwise
+    var scrollable: App.Scrollable = .{ .container = box };
     try container.append(try App.Container.init(allocator, .{}, scrollable.element()));
 
     try app.start();