Feat: text selection using mouse

src/state/editor.rs

@@ -99,6 +99,7 @@ pub struct EditorContext {
     pub stack_cache: RefCell<Option<StackCache>>,
     pub target: EditorTarget,
     pub steps_per_page: Cell<usize>,
+    pub mouse_selecting: bool,
 }
 
 #[derive(Clone)]
@@ -150,6 +151,7 @@ impl Default for EditorContext {
             stack_cache: RefCell::new(None),
             target: EditorTarget::default(),
             steps_per_page: Cell::new(32),
+            mouse_selecting: false,
         }
     }
 }