InputText: Internal: added reload from user-buf feature. (#2890)

Very highly requested feature (#6962, #5219, #3290, #4627, #5054, #3878, #2881, #1506, #1216, #968).
Also useful for interactive completion/selection popups (#2057, #718)
Based on @kudaba PR. Design for Inputtext V2 should make this obsolete.

imgui.cpp

@@ -12257,6 +12257,8 @@ void ImGui::NavMoveRequestApplyResult()
         g.NavWindow = result->Window;
         g.NavLastValidSelectionUserData = ImGuiSelectionUserData_Invalid;
     }
+
+    // FIXME: Could become optional e.g. ImGuiNavMoveFlags_NoClearActiveId if we later want to apply navigation requests without altering active input.
     if (g.ActiveId != result->ID)
         ClearActiveID();