[Macros] Requestify MacroExpansionExpr expansion

The request returns the expanded buffer ID even if it failed to
typecheck the expanded buffer.
This makes refactoring 'Expand Macro' work regardless of the
typechecking results.

rdar://108530760

include/swift/AST/TypeCheckRequests.h

@@ -3930,6 +3930,26 @@ public:
   void noteCycleStep(DiagnosticEngine &diags) const;
 };
 
+/// Expand a 'MacroExpansionExpr',
+class ExpandMacroExpansionExprRequest
+    : public SimpleRequest<ExpandMacroExpansionExprRequest,
+                           Optional<unsigned>(MacroExpansionExpr *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  Optional<unsigned>
+  evaluate(Evaluator &evaluator, MacroExpansionExpr *mee) const;
+
+public:
+  bool isCached() const { return true; }
+  void diagnoseCycle(DiagnosticEngine &diags) const;
+  void noteCycleStep(DiagnosticEngine &diags) const;
+};
+
 /// Expand all accessor macros attached to the given declaration.
 ///
 /// Produces the set of macro expansion buffer IDs.

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -439,6 +439,9 @@ SWIFT_REQUEST(TypeChecker, ExternalMacroDefinitionRequest,
 SWIFT_REQUEST(TypeChecker, ExpandMacroExpansionDeclRequest,
               ArrayRef<Decl *>(MacroExpansionDecl *),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, ExpandMacroExpansionExprRequest,
+              ArrayRef<Decl *>(MacroExpansionExpr *),
+              Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ExpandMemberAttributeMacros,
               ArrayRef<unsigned>(Decl *),
               Cached, NoLocationInfo)