[SourceKit] Compute code completion type relation when wrapping a ContextFreeCodeCompletionResult in a CodeCompletionResult

[CodeCompletion] Make ExpectedTypeContext a class with explicit getters/setters

This simplifies debugging because you can break when the possible types are set and you can also search for references to `setPossibleType` to figure out where the expected types are being set.

tools/SourceKit/lib/SwiftLang/SwiftCompletion.cpp

@@ -923,14 +923,15 @@ static void transformAndForwardResults(
         new (innerSink.allocator) ContextFreeCodeCompletionResult(
             CodeCompletionResultKind::BuiltinOperator, completionString,
             CodeCompletionOperatorKind::None,
-            /*BriefDocComment=*/"", ContextFreeNotRecommendedReason::None,
+            /*BriefDocComment=*/"", CodeCompletionResultType::notApplicable(),
+            ContextFreeNotRecommendedReason::None,
             CodeCompletionDiagnosticSeverity::None,
             /*DiagnosticMessage=*/"");
     auto *paren = new (innerSink.allocator) CodeCompletion::SwiftResult(
         *contextFreeResult, SemanticContextKind::CurrentNominal,
         CodeCompletionFlairBit::ExpressionSpecific,
         exactMatch ? exactMatch->getNumBytesToErase() : 0,
-        CodeCompletionResultTypeRelation::NotApplicable,
+        /*TypeContext=*/nullptr, /*DC=*/nullptr,
         ContextualNotRecommendedReason::None,
         CodeCompletionDiagnosticSeverity::None, /*DiagnosticMessage=*/"");