Remove fixed size buffer when reading lines from the response file.

[jlaanstra]

This PR removes a hardcoded maximum line length and instead, dynamically allocates a string to read lines.

Currently cppwinrt.exe silently fails. @kennykerr thoughts on outputting some kind of error when the response file contains invalid data?

[kennykerr]

You can report errors using throw_invalid().

[jlaanstra]

Looks like that might be handled already as it hits the same code path as if it was passed in without a response file.

[kennykerr]

Thanks Johan!