Include popups and tooltips in Harness::fit_contents (#7556)

This makes `Harness::fit_contents` also use popups and tooltips to
compute the size of the contents.

crates/egui_kittest/tests/snapshots/test_tooltip_hidden.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:025942c144891b8862bf931385824e0484e60f4e7766f5d4401511c72ff20756
+size 2975

crates/egui_kittest/tests/snapshots/test_tooltip_shown.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c267530452adb4f1ed1440df476d576ef4c2d96e6c58068bb57fed4615f5e113
+size 4453

crates/egui_kittest/tests/tests.rs

@@ -16,6 +16,28 @@ fn test_shrink() {
     harness.snapshot("test_shrink");
 }
 
+#[test]
+fn test_tooltip() {
+    let mut harness = Harness::new_ui(|ui| {
+        ui.label("Hello, world!");
+        ui.separator();
+        ui.label("This is a test")
+            .on_hover_text("This\nis\na\nvery\ntall\ntooltip!");
+    });
+
+    harness.fit_contents();
+
+    #[cfg(all(feature = "snapshot", feature = "wgpu"))]
+    harness.snapshot("test_tooltip_hidden");
+
+    harness.get_by_label("This is a test").hover();
+    harness.run_ok();
+    harness.fit_contents();
+
+    #[cfg(all(feature = "snapshot", feature = "wgpu"))]
+    harness.snapshot("test_tooltip_shown");
+}
+
 #[test]
 fn test_modifiers() {
     #[derive(Default)]