regexp: ensure that the bytecode size grows linearly with respect to

regexp: ensure that the bytecode size grows linearly with respect to
the input regexp.

This way, pathological regexps such as
/(:?(:?(:?(:?(:?(:?(:?(:?(:?(:?(:?(:?(:?(?:a|)+|)+|)+|)+|)+|)+|)+|)+|)+|)+|)+|)+|)+|)+/ are no longer an issue. The generated bytecode is also simpler and
faster.