MultiSelect: move HasSelectionData to ImGuiItemFlags to facilitate copying around in standardized fieds.

Required/motivated to simplify support for ImGuiTreeNodeFlags_NavLeftJumpsBackHere (bc3c0ce) in this branch.

imgui_internal.h

@@ -1211,15 +1211,14 @@ enum ImGuiNextItemDataFlags_
     ImGuiNextItemDataFlags_HasOpen      = 1 << 1,
     ImGuiNextItemDataFlags_HasShortcut  = 1 << 2,
     ImGuiNextItemDataFlags_HasRefVal    = 1 << 3,
-    ImGuiNextItemDataFlags_HasSelectionData = 1 << 4,
 };
 
 struct ImGuiNextItemData
 {
     ImGuiNextItemDataFlags      Flags;
-    ImGuiItemFlags              ItemFlags;          // Currently only tested/used for ImGuiItemFlags_AllowOverlap.
+    ImGuiItemFlags              ItemFlags;          // Currently only tested/used for ImGuiItemFlags_AllowOverlap and ImGuiItemFlags_HasSelectionUserData.
     // Non-flags members are NOT cleared by ItemAdd() meaning they are still valid during NavProcessItem()
-    ImGuiID                     FocusScopeId;       // Set by SetNextItemSelectionUserData() (!= 0 signify value has been set)
+    ImGuiID                     FocusScopeId;       // Set by SetNextItemSelectionUserData()
     ImGuiSelectionUserData      SelectionUserData;  // Set by SetNextItemSelectionUserData() (note that NULL/0 is a valid value, we use -1 == ImGuiSelectionUserData_Invalid to mark invalid values)
     float                       Width;              // Set by SetNextItemWidth()
     ImGuiKeyChord               Shortcut;           // Set by SetNextItemShortcut()

imgui_widgets.cpp

@@ -6390,8 +6390,8 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiID storage_id, ImGuiTreeNodeFlags
     }
 
     // Compute open and multi-select states before ItemAdd() as it clear NextItem data.
+    const bool is_multi_select = (g.NextItemData.ItemFlags & ImGuiItemFlags_IsMultiSelect) != 0; // Before ItemAdd()
     bool is_open = TreeNodeUpdateNextOpen(storage_id, flags);
-    const bool is_multi_select = (g.NextItemData.Flags & ImGuiNextItemDataFlags_HasSelectionData) != 0; // Before ItemAdd()
     bool item_add = ItemAdd(interact_bb, id);
     g.LastItemData.StatusFlags |= ImGuiItemStatusFlags_HasDisplayRect;
     g.LastItemData.DisplayRect = frame_bb;
@@ -6780,7 +6780,7 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     }
 
     const bool disabled_item = (flags & ImGuiSelectableFlags_Disabled) != 0;
-    const bool is_multi_select = (g.NextItemData.Flags & ImGuiNextItemDataFlags_HasSelectionData) != 0; // Before ItemAdd()
+    const bool is_multi_select = (g.NextItemData.ItemFlags & ImGuiItemFlags_IsMultiSelect) != 0; // Before ItemAdd()
     const bool item_add = ItemAdd(bb, id, NULL, disabled_item ? (ImGuiItemFlags)ImGuiItemFlags_Disabled : ImGuiItemFlags_None);
 
     if (span_all_columns)