const correctness for Combo and ListBox

Since Combo and ListBox only read and display the list of items, they
should not modify the pointers inside the array of pointers passed in.
Adding "const" here makes it possible to call these functions with such
an array of const pointers. Previously, a cast to "const char**" was
required as a workaround, otherwise there was a compile error.

imgui.cpp

@@ -8399,7 +8399,7 @@ bool ImGui::InputInt4(const char* label, int v[4], ImGuiInputTextFlags extra_fla
 
 static bool Items_ArrayGetter(void* data, int idx, const char** out_text)
 {
-    const char** items = (const char**)data;
+    const char* const* items = (const char* const*)data;
     if (out_text)
         *out_text = items[idx];
     return true;
@@ -8426,7 +8426,7 @@ static bool Items_SingleStringGetter(void* data, int idx, const char** out_text)
 }
 
 // Combo box helper allowing to pass an array of strings.
-bool ImGui::Combo(const char* label, int* current_item, const char** items, int items_count, int height_in_items)
+bool ImGui::Combo(const char* label, int* current_item, const char* const* items, int items_count, int height_in_items)
 {
     const bool value_changed = Combo(label, current_item, Items_ArrayGetter, (void*)items, items_count, height_in_items);
     return value_changed;
@@ -8703,7 +8703,7 @@ void ImGui::ListBoxFooter()
     EndGroup();
 }
 
-bool ImGui::ListBox(const char* label, int* current_item, const char** items, int items_count, int height_items)
+bool ImGui::ListBox(const char* label, int* current_item, const char* const* items, int items_count, int height_items)
 {
     const bool value_changed = ListBox(label, current_item, Items_ArrayGetter, (void*)items, items_count, height_items);
     return value_changed;

imgui.h

@@ -265,7 +265,7 @@ namespace ImGui
     IMGUI_API bool          CheckboxFlags(const char* label, unsigned int* flags, unsigned int flags_value);
     IMGUI_API bool          RadioButton(const char* label, bool active);
     IMGUI_API bool          RadioButton(const char* label, int* v, int v_button);
-    IMGUI_API bool          Combo(const char* label, int* current_item, const char** items, int items_count, int height_in_items = -1);
+    IMGUI_API bool          Combo(const char* label, int* current_item, const char* const* items, int items_count, int height_in_items = -1);
     IMGUI_API bool          Combo(const char* label, int* current_item, const char* items_separated_by_zeros, int height_in_items = -1);      // separate items with \0, end item-list with \0\0
     IMGUI_API bool          Combo(const char* label, int* current_item, bool (*items_getter)(void* data, int idx, const char** out_text), void* data, int items_count, int height_in_items = -1);
     IMGUI_API bool          ColorButton(const ImVec4& col, bool small_height = false, bool outline_border = true);
@@ -339,7 +339,7 @@ namespace ImGui
     // Widgets: Selectable / Lists
     IMGUI_API bool          Selectable(const char* label, bool selected = false, ImGuiSelectableFlags flags = 0, const ImVec2& size = ImVec2(0,0));  // size.x==0.0: use remaining width, size.x>0.0: specify width. size.y==0.0: use label height, size.y>0.0: specify height
     IMGUI_API bool          Selectable(const char* label, bool* p_selected, ImGuiSelectableFlags flags = 0, const ImVec2& size = ImVec2(0,0));
-    IMGUI_API bool          ListBox(const char* label, int* current_item, const char** items, int items_count, int height_in_items = -1);
+    IMGUI_API bool          ListBox(const char* label, int* current_item, const char* const* items, int items_count, int height_in_items = -1);
     IMGUI_API bool          ListBox(const char* label, int* current_item, bool (*items_getter)(void* data, int idx, const char** out_text), void* data, int items_count, int height_in_items = -1);
     IMGUI_API bool          ListBoxHeader(const char* label, const ImVec2& size = ImVec2(0,0)); // use if you want to reimplement ListBox() will custom data or interactions. make sure to call ListBoxFooter() afterwards.
     IMGUI_API bool          ListBoxHeader(const char* label, int items_count, int height_in_items = -1); // "