[clang] [NFC] Factor out common parts of ArraySections into its own class (PR #89639)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I opted to leave the type of both array sections the same as it seems like it will save a bunch of work and complexity, at the expense of 1 'print', and potentially 1 diagnostic.  Let me know if you think this is an important distinction!

https://github.com/llvm/llvm-project/pull/89639