fix(util/script_exception): make sure a script_nested_exception may have a nested script_nested_exception, use LEAN_THREAD_LOCAL macro instead of thread_local

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/script_exception): make sure a script_nested_exception may have a nested script_nested_exception, use LEAN_THREAD_LOCAL macro instead of thread_local