[CS] Record IgnoreInvalidASTNode for invalid key path component

And ensure we don't end up with invalid key paths in CSApply.

Author: hamishknight

lib/Sema/CSApply.cpp

@@ -5395,19 +5395,18 @@ namespace {
           }
           break;
         }
-        case KeyPathExpr::Component::Kind::Invalid:
-        case KeyPathExpr::Component::Kind::CodeCompletion: {
-          auto component = origComponent;
-          component.setComponentType(leafTy);
-          resolvedComponents.push_back(component);
-          break;
-        }
         case KeyPathExpr::Component::Kind::Identity: {
           auto component = origComponent;
           component.setComponentType(componentTy);
           resolvedComponents.push_back(component);
           break;
         }
+        case KeyPathExpr::Component::Kind::CodeCompletion:
+          llvm_unreachable("solver-based completion shouldn't do CSApply");
+          break;
+        case KeyPathExpr::Component::Kind::Invalid:
+          llvm_unreachable("should have been diagnosed");
+          break;
         case KeyPathExpr::Component::Kind::Member:
         case KeyPathExpr::Component::Kind::Subscript:
         case KeyPathExpr::Component::Kind::Apply:

lib/Sema/CSGen.cpp

@@ -3845,6 +3845,7 @@ namespace {
 
         switch (auto kind = component.getKind()) {
         case KeyPathExpr::Component::Kind::Invalid:
+          CS.recordFix(IgnoreInvalidASTNode::create(CS, memberLocator));
           break;
         case KeyPathExpr::Component::Kind::CodeCompletion:
           // We don't know what the code completion might resolve to, so we are