[CodeCompletion] Don't check 'InvalidAsyncContext' for imported globals

'InvalidAsyncContext' depends on the decl context. That may case
"sticky" not-recommended If it's cached for a non-async context.

To workaround this, stop checking 'InvalidAsyncContext' when collecting
completion items for caching. Also consistently use the 'SourceFile' as
the decl context to avoid decl context specific behavior.

rdar://78315441

lib/IDE/CodeCompletionCache.cpp

@@ -342,6 +342,10 @@ static void writeCachedModule(llvm::raw_ostream &out,
     endian::Writer LE(results, little);
     for (CodeCompletionResult *R : V.Sink.Results) {
       assert(!R->isArgumentLabels() && "Argument labels should not be cached");
+      assert(R->getNotRecommendedReason() !=
+             CodeCompletionResult::NotRecommendedReason::InvalidAsyncContext &&
+             "InvalidAsyncContext is decl context specific, cannot be cached");
+
       // FIXME: compress bitfield
       LE.write(static_cast<uint8_t>(R->getKind()));
       if (R->getKind() == CodeCompletionResult::Declaration)