Disable error handler with constant

It would be great if the debug bar error handler could be disabled using a constant, so I can use my own custom error handler.
(it works for query monitor like this already using: define( ‘QM_DISABLE_ERROR_HANDLER’, true );

File class-debug-bar-php.php => set_error_handler( would need to be wrapped in condition for it to work.

It’s a really simple but helpful change.