[mlir][Index][NFC] Migrate index dialect to the new fold API

See https://discourse.llvm.org/t/psa-new-improved-fold-method-signature-has-landed-please-update-your-downstream-projects/67618 for context

Similar to the patch for the arith dialect, the index dialects fold implementations make heavy use of generic fold functions, hence the change being comparatively mechanical and mostly changing the function signature.

Differential Revision: https://reviews.llvm.org/D141502