[LLDB][GUI] Handle extra navigation keys in forms

This patch handles the up and down keys if they weren't handled by the
selected field. Moreover, it makes sure the form always absorb the key
to take full control until the form is canceled or submitted.

Differential Revision: https://reviews.llvm.org/D108414

lldb/source/Core/IOHandlerCursesGUI.cpp

@@ -2801,6 +2801,8 @@ public:
     }
   }
 
+  // Always return eKeyHandled to absorb all events since forms are always
+  // added as pop-ups that should take full control until canceled or submitted.
   HandleCharResult WindowDelegateHandleChar(Window &window, int key) override {
     switch (key) {
     case '\r':
@@ -2815,9 +2817,11 @@ public:
       ExecuteAction(window, 0);
       return eKeyHandled;
     case '\t':
-      return SelectNext(key);
+      SelectNext(key);
+      return eKeyHandled;
     case KEY_SHIFT_TAB:
-      return SelectPrevious(key);
+      SelectPrevious(key);
+      return eKeyHandled;
     case KEY_ESCAPE:
       window.GetParent()->RemoveSubWindow(&window);
       return eKeyHandled;
@@ -2829,10 +2833,24 @@ public:
     // to that field.
     if (m_selection_type == SelectionType::Field) {
       FieldDelegate *field = m_delegate_sp->GetField(m_selection_index);
-      return field->FieldDelegateHandleChar(key);
+      if (field->FieldDelegateHandleChar(key) == eKeyHandled)
+        return eKeyHandled;
     }
 
-    return eKeyNotHandled;
+    // If the key wasn't handled by the possibly selected field, handle some
+    // extra keys for navigation.
+    switch (key) {
+    case KEY_DOWN:
+      SelectNext(key);
+      return eKeyHandled;
+    case KEY_UP:
+      SelectPrevious(key);
+      return eKeyHandled;
+    default:
+      break;
+    }
+
+    return eKeyHandled;
   }
 
 protected: