[CodeCompletion] Don't mark #keyPath as "expression specific" without #

We suggest #keyPath in every String context, so having it be
expression-specific is artificially increasing its priority.

rdar://problem/26544672

lib/IDE/CodeCompletion.cpp

@@ -2196,11 +2196,15 @@ public:
     // #keyPath is only available when the Objective-C runtime is.
     if (!Ctx.LangOpts.EnableObjCInterop) return;
 
+    // After #, this is a very likely result. When just in a String context,
+    // it's not.
+    auto semanticContext = needPound ? SemanticContextKind::None
+                                     : SemanticContextKind::ExpressionSpecific;
+
     CodeCompletionResultBuilder Builder(
                                   Sink,
                                   CodeCompletionResult::ResultKind::Keyword,
-                                  SemanticContextKind::ExpressionSpecific,
-                                  ExpectedTypes);
+                                  semanticContext, ExpectedTypes);
     if (needPound)
       Builder.addTextChunk("#keyPath");
     else