Move access-path filtering into ModuleNameLookup (out of lookupValue) (#27097)

Removes duplicated logic from the implementations of
FileUnit::lookupValue, and simplifies the interface to
ModuleDecl::lookupValue, where everyone was passing an empty
(non-filtering) access path anyway /except/ during actual lookup from
source code. No functionality change.

lib/Serialization/Serialization.cpp

@@ -3653,8 +3653,7 @@ static TypeAliasDecl *findTypeAliasForBuiltin(ASTContext &Ctx, Type T) {
   StringRef TypeName = FullName.substr(8);
 
   SmallVector<ValueDecl*, 4> CurModuleResults;
-  Ctx.TheBuiltinModule->lookupValue(ModuleDecl::AccessPathTy(),
-                                    Ctx.getIdentifier(TypeName),
+  Ctx.TheBuiltinModule->lookupValue(Ctx.getIdentifier(TypeName),
                                     NLKind::QualifiedLookup,
                                     CurModuleResults);
   assert(CurModuleResults.size() == 1);