[clang-offload-bundler][NFC] Library-ize ClangOffloadBundler (4/4)

[lamb-j]

Summary

Lifting the core functionalities of the clang-offload-bundler into a
user-facing library/API.

This NFC patch (4/4) moves the API files from
clang/tools/clang-offload-bundler into clang/lib/Driver and
clang/include/clang/Driver.