These new operations match the semantics of
llvm.experimental.vector.insert and llvm.experimental.vector.extract.
`vector.scalable.insert_1d` and `vector.extract_1d` allow, respectively, insertscalable.extract` allow,
fixed-lengthrespectively, insert vectors into scalable vectors, and extract fixed-lengthvectors
vectors from scalable vectors.
The discussion about the inclusion of these operations is here:
https://discourse.llvm.org/t/rfc-interfacing-between-fixed-length-and-scalable-vectors-for-vls-vector-code-on-scalable-vector-architectures