* Add support for JSONPath with '$' prefix and integrate into dom::at_path (#2266)
- Updated `json_path_to_pointer_conversion` to support JSONPath starting with the '$' prefix, while maintaining compatibility with the existing implementation.
- Moved `json_path_to_pointer_conversion` to a separate header file for better modularity and to support JSONPath queries in `dom` mode.
- Implemented `at_path` functionality in `dom` mode to enable querying JSON using JSONPath.
- Added unit tests to validate the new JSONPath support in `dom` mode and ensure compatibility with both standard and existing JSONPath formats.
* two minor fixes
* more tests and documentation
* damn compiler warnings
* more documentation fixes
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Co-authored-by: Zhengguo Yang <yangzhgg@gmail.com>
huangqinjin