This commit adds a test case that performs two back-to-back 1:N
replacements: `(i16) -> (i16, i16) -> ((i16, i16), (i16, i16))`. For the
moment, 3 argument materializations are inserted. In the future (when
the conversion value mapping supports 1:N), a single target
materialization will be inserted. Addresses a
[comment](https://github.com/llvm/llvm-project/pull/116524#discussion_r1894629711)
in #116524.
412e30b227