[clang][cli] Round-trip the whole CompilerInvocation

Finally, this patch moves from round-tripping one `CompilerInvocation` at a time to round-tripping the invocation as a whole.

This patch includes only the code required to make round-tripping the whole invocation work. More cleanups will be done in a follow-up patch.

Depends on D96847, D97041 & D97042.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D96280