Enhance support for FY-3F/MERSI-3

This PR enhanced support for FY-3F/MERSI-3 data. Includes fixed geolocation dataset name in 250m data, support get coefficients, etc. Actually, I'm not sure whether the test config is correct. theoretically, this test is basically the same as the FY-3D.

• [x] Tests added
• [ ] Fully documented
• [ ] Add your name to AUTHORS.md if not there already

I read the official document incorrectly, the part of geolocation data was originally correct, so I reverted the corresponding changes. The remaining enhancement to get coefficients is ok