[clangd] Properly set filterText for index-based completion items

It was previously set to an identifier that the user typed, leading to
surprising behavior in VSCode (probably in other editors too).

llvm-svn: 321554
diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
index 87f73b2..28ea4db 100644
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -558,7 +558,7 @@
   Item.insertText = Sym.Name;
   // FIXME(ioeric): support snippets.
   Item.insertTextFormat = InsertTextFormat::PlainText;
-  Item.filterText = Filter;
+  Item.filterText = Sym.Name;
 
   // FIXME(ioeric): sort symbols appropriately.
   Item.sortText = "";