[flang][fir] Add array value operations.
We lower expressions with rank > 0 to a set of high-level array operations.
These operations are then analyzed and refined to more primitve
operations in subsequent pass(es).
This patch upstreams these array operations and some other helper ops.
Authors: Eric Schweitz, Rajan Walia, Kiran Chandramohan, et.al.
Differential Revision: https://reviews.llvm.org/D97421