Adds initial support for copyable elements. This patch only models adds
and model copyable elements as add <element>, 0, i.e. uses identity
constants for missing lanes.
Only support for elements, which do not require scheduling, is added to
reduce size of the patch.
Fixed compile time regressions, updated release notes
Reviewers: RKSimon, hiraditya
Reviewed By: RKSimon
Pull Request: https://github.com/llvm/llvm-project/pull/140279
898bba311f