Wrap docstring comments in raw string formatting
Per:
Pure autopybind11 issue: Docstrings should be escaped or surrounded with unlikely-to-be-copied tokens.
For Drake, we use the following literals: https://drake.mit.edu/styleguide/cppguide.html#Raw_String_Literals
Example from mkdoc test: https://github.com/RobotLocomotion/drake/blob/v0.27.0/tools/workspace/pybind11/test/sample_header_documentation.expected.h#L20-L21