LibJS/Bytecode: Improve export statement handling

This adds support for exporting class expressions, which was previously
TODO'd.

We now correctly set the binding name of exports to `"*default*"` if
they are unnamed. I'm not sure what the difference between the
`InitializationMode` kinds is, but using `Initialize` fixes a bunch of
tests.

Note that some export tests (e.g. `eval-export-dflt-expr-cls-named.js`)
still fail, as we don't set the "name" property of exported classes
correctly.

176 new passes on test262

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -2857,13 +2857,18 @@ Bytecode::CodeGenerationErrorOr<void> ExportStatement::generate_bytecode(Bytecod
     }
 
     if (is<ClassExpression>(*m_statement)) {
-        TODO();
+        TRY(m_statement->generate_bytecode(generator));
+
+        if (!static_cast<ClassExpression const&>(*m_statement).has_name())
+            generator.emit<Bytecode::Op::SetVariable>(generator.intern_identifier(ExportStatement::local_name_for_default), Bytecode::Op::SetVariable::InitializationMode::Initialize);
+
+        return {};
     }
 
     // ExportDeclaration : export default AssignmentExpression ;
     VERIFY(is<Expression>(*m_statement));
     TRY(generator.emit_named_evaluation_if_anonymous_function(static_cast<Expression const&>(*m_statement), DeprecatedFlyString("default"sv)));
-    generator.emit<Bytecode::Op::SetVariable>(generator.intern_identifier("default"sv));
+    generator.emit<Bytecode::Op::SetVariable>(generator.intern_identifier(ExportStatement::local_name_for_default), Bytecode::Op::SetVariable::InitializationMode::Initialize);
     return {};
 }