Multiple binaries have the needs to open input files. Use this function
to de-duplicate the code.
Also changed openOutputFile() to return errors using std::string since
it is a library call and accessing I/O in library call is not friendly.
PiperOrigin-RevId: 228878221
This has been a long-standing TODO in the build system. Now that we need to
share the non-inlined implementation of file utilities for translators, create
a separate library for support functionality. Move Support/* headers to the
new library in the build system.
PiperOrigin-RevId: 222398880