[Macros] Ensure that we compute the interface type before we add accessors

Adding accessors to a stored property, which removes its initializer.
Force computation of the interface type first.

There are better ways to model this in the AST, but it requires
reworking how we handle initializers to break them into requests.

(cherry picked from commit ef7970b)

Author: DougGregor

lib/Sema/TypeCheckMacros.cpp

@@ -1330,6 +1330,7 @@ evaluateAttachedMacro(MacroDecl *macro, Decl *attachedTo, CustomAttr *attr,
 Optional<unsigned> swift::expandAccessors(
     AbstractStorageDecl *storage, CustomAttr *attr, MacroDecl *macro
 ) {
+  (void)storage->getInterfaceType();
   // Evaluate the macro.
   auto macroSourceFile = evaluateAttachedMacro(macro, storage, attr,
                                                /*passParentContext*/false,