LibJS: Clear compile-only data from SharedFunctionInstanceData

After successful bytecode compilation, the m_functions_to_initialize
and m_var_names_to_initialize_binding vectors are no longer needed
as they are only consumed by emit_function_declaration_instantiation()
during code generation.

Add clear_compile_inputs() to release these vectors post-compile,
and call it from both ECMAScriptFunctionObject::get_stack_frame_size()
and NativeJavaScriptBackedFunction::bytecode_executable() after their
respective lazy compilation succeeds.

Also add a pre-compile assertion in Generator::generate_from_function()
to verify we never try to compile the same function data twice, and a
VERIFY in ECMAScriptFunctionObject::ecmascript_code() to guard against
null dereference.

Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -261,6 +261,7 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::get_stack_frame_size(size_t& r
         } else {
             executable = TRY(Bytecode::compile(vm(), shared_data(), Bytecode::BuiltinAbstractOperationsEnabled::No));
         }
+        m_shared_data->clear_compile_inputs();
     }
     registers_and_locals_count = executable->registers_and_locals_count;
     constants_count = executable->constants.size();