[IDE] Add nonisolated(nonsending) to completion lookup

Seems we perhaps missed adding the completion for `nonsending` here?

cc @xedin

[IDE] Tests: That that `nonisolated` has `nonsending` completion

Author: ktoso

lib/IDE/CompletionLookup.cpp

@@ -3139,6 +3139,7 @@ void CompletionLookup::getAttributeDeclParamCompletions(
     break;
   case ParameterizedDeclAttributeKind::Nonisolated:
     addDeclAttrParamKeyword("unsafe", /*Parameters=*/{}, "", false);
+    addDeclAttrParamKeyword("nonsending", /*Parameters=*/{}, "", false);
     break;
   case ParameterizedDeclAttributeKind::AccessControl:
     addDeclAttrParamKeyword("set", /*Parameters=*/{}, "", false);

test/IDE/complete_nonisolated.swift

@@ -0,0 +1,10 @@
+// RUN: %batch-code-completion
+
+// NONISOLATED-DAG: Keyword/None:                       unsafe; name=unsafe
+// NONISOLATED-DAG: Keyword/None:                       nonsending; name=nonsending
+
+nonisolated(#^NONISOLATED_UNSAFE_TOP_LEVEL?check=NONISOLATED^#) var count = 0
+
+struct MyStruct {
+  nonisolated(#^NONISOLATED_UNSAFE_IN_STRUCT?check=NONISOLATED^#) var prop = 0
+}