[clang][cli] Generate HeaderSearch options separately

This patch moves parsing of header search options from `generateCC1Options` to separate `GenerateHeaderSearchArgs`.

The round-trip algorithm in D94472 requires this separation to be able to run parsing and generating **only** for the options that need to be tested via round-tripping.

This also moves the `GENERATE_OPTION_WITH_MARSHALLING` to the top of the file, because other kinds of options will be generated in separate functions that will be spread throughout `CompilerInvocation.cpp` to be close to their parsing counterparts.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D94803