Fix clone of module export decl (#4329)

Fixes #4328

### Changes
Fix clone method of ModuleExportDecl

### Testing
No tests added.

Instead, we should run part of the testsuite using the IDE instead of
the CLI, since the IDE runs additional code (caching code, which
currently uses cloning, which isn't tested well)

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is made under the terms of the [MIT
license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>

Source/DafnyCore/AST/Modules/ModuleExportDecl.cs

@@ -30,6 +30,7 @@ public ModuleExportDecl(Cloner cloner, ModuleExportDecl original, ModuleDefiniti
  ProvideAll = original.ProvideAll;
  RevealAll = original.RevealAll;
  IsRefining = original.IsRefining;
+ IsDefault = original.IsDefault;
  ThisScope = new VisibilityScope(FullSanitizedName);
  }
 

docs/dev/news/fix.4328

@@ -0,0 +1 @@
+Fix issue that would prevent the IDE from correctly handling default export sets