feat(terminal/osc12): define cursor color through style of cell that describes the cursor position

The `.default` color will reset the cursor color to the terminal's default color

examples/elements/button.zig

@@ -102,7 +102,7 @@ pub fn main() !void {
     }, quit_text.element());
     defer container.deinit();
 
-    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .light_grey } }, element));
+    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .lightgrey } }, element));
     try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .black } }, button.element()));
 
     try app.start();