InnerClipRect use ImFloor() matching docking branch (fix c41868531 for #6861, #2884, followed by rename 94da5842)

Since negative windows can never be visibile in master it didn't show as a difference.

imgui.cpp

@@ -6845,10 +6845,10 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         // Affected by window/frame border size. Used by:
         // - Begin() initial clip rect
         float top_border_size = (((flags & ImGuiWindowFlags_MenuBar) || !(flags & ImGuiWindowFlags_NoTitleBar)) ? style.FrameBorderSize : window->WindowBorderSize);
-        window->InnerClipRect.Min.x = ImTrunc(0.5f + window->InnerRect.Min.x + ImMax(ImTrunc(window->WindowPadding.x * 0.5f), window->WindowBorderSize));
-        window->InnerClipRect.Min.y = ImTrunc(0.5f + window->InnerRect.Min.y + top_border_size);
-        window->InnerClipRect.Max.x = ImTrunc(0.5f + window->InnerRect.Max.x - ImMax(ImTrunc(window->WindowPadding.x * 0.5f), window->WindowBorderSize));
-        window->InnerClipRect.Max.y = ImTrunc(0.5f + window->InnerRect.Max.y - window->WindowBorderSize);
+        window->InnerClipRect.Min.x = ImFloor(0.5f + window->InnerRect.Min.x + ImMax(ImTrunc(window->WindowPadding.x * 0.5f), window->WindowBorderSize));
+        window->InnerClipRect.Min.y = ImFloor(0.5f + window->InnerRect.Min.y + top_border_size);
+        window->InnerClipRect.Max.x = ImFloor(0.5f + window->InnerRect.Max.x - ImMax(ImTrunc(window->WindowPadding.x * 0.5f), window->WindowBorderSize));
+        window->InnerClipRect.Max.y = ImFloor(0.5f + window->InnerRect.Max.y - window->WindowBorderSize);
         window->InnerClipRect.ClipWithFull(host_rect);
 
         // Default item width. Make it proportional to window size if window manually resizes