Fix picking mode on outside-node-input container, so that invisible stuff doesn't block click events

Match slot colors for outside-node-inputs

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/PortInputView.cs

 
         public PortInputView(MaterialSlot slot)
         {
+            pickingMode = PickingMode.Ignore;
             ClearClassList();
             m_Slot = slot;
             m_SlotType = slot.concreteValueType;

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Resources/Styles/MaterialGraph.uss

 PortInputView > #container > #slot {
     width: 8;
     height: 8;
-    background-color: #000000;
+    background-color: #2B2B2B;
+    border-color: #232323;
+    border-top-width: 1;
+    border-bottom-width: 1;
+    border-left-width: 1;
+    border-right-width: 1;
     border-radius: 4;
     margin-left: 6;
     margin-right: 6;