tree: move common code out of ToplevelNode trait

src/it/tests/t0010_fullscreen_focus.rs

@@ -1,7 +1,7 @@
 use {
     crate::{
         it::{test_error::TestError, testrun::TestRun},
-        tree::ToplevelNode,
+        tree::ToplevelNodeBase,
     },
     std::rc::Rc,
 };

src/it/tests/t0014_container_scroll_focus.rs

@@ -4,7 +4,7 @@ use {
             test_error::{TestErrorExt, TestResult},
             testrun::TestRun,
         },
-        tree::ToplevelNode,
+        tree::ToplevelNodeBase,
     },
     jay_config::Axis,
     std::rc::Rc,

src/it/tests/t0015_scroll_partial.rs

@@ -1,7 +1,7 @@
 use {
     crate::{
         it::{test_error::TestResult, testrun::TestRun},
-        tree::ToplevelNode,
+        tree::ToplevelNodeBase,
     },
     std::rc::Rc,
 };