Unparseable docstrings should fall back to the old docstring parser

[rchiodo]

We currently attempt to recover parser errors in https://github.com/microsoft/pyrx/blob/8d88e0bba6789cec3a57d3e6efad45df11873d56/packages/pylance-internal/src/common/docstring/fixer.ts#L560

This can sometimes work but there are likely an infinite number of cases that we cannot parse. In all of those cases we currently just stop showing any more output.

I think we should instead switch back to the old docstring parser and we have any unrecoverable errors.

See this issue for an example:
#6419