[llvm][TextAPI/MachO] Extend TBD_V3 unittest to verify writing

The existing unit tests cover a wide variety of reading TBD files but
lack coverages on the writing side. Case in point is the macCatalyst
case which we're able to read, but not write.

This patch extends the unit test dealing with valid input to write their
content again to verify the writer.

Differential revision: https://reviews.llvm.org/D73328