[MachOYAML] Improve section offset misalignment error message

Before:
```
wrote too much data somewhere, section offsets don't line up
```

After:
```
wrote too much data somewhere, section offsets in section __debug_str for segment __DWARF don't line up: [cursor=0x581], [fileStart=0x0], [sectionOffset=0x579]
```

Differential Revision: https://reviews.llvm.org/D140116