[llvm] ADT/Matrix: two-dimensional Container with View (PR #98893)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

Same high-level comment as in https://github.com/llvm/llvm-project/pull/98895/files#r1681176240: could we make this code local to its first user before promoting to ADT?

https://github.com/llvm/llvm-project/pull/98893