Fixed mouse pointer mismatch on FilteredMenu

Part (the part with informative text) of the filter input control was showing arrow mouse pointer, instead of the text input pointer. Now the whole control shows the expected pointer.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=157597019

closure/goog/css/filteredmenu.css

@@ -18,6 +18,7 @@
 
 .goog-menu-filter div {
   color: gray;
+  pointer-events: none;
   position: absolute;
   padding: 1px;
 }