[mlir] [VectorOps] Implement vector tuple get folding

Summary: Rewrites get-i tup<a1,...,an> into ai

Reviewers: nicolasvasilache, rriddle, andydavis1

Reviewed By: nicolasvasilache, rriddle, andydavis1

Subscribers: merge_guards_bot, mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, arpith-jacob, mgester, lucyrfox, liufengdb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73213