[CIR] Fix problems with stale insert locations (#197296)
This change fixes three places where we were copying the builder rather
than getting a reference to it, leading to potential problems with
incorrect state, including insert locations. Two of these cases were
causing observable problems, and I'm adding regression tests for those.
The third doesn't seem to have caused any actual problems, but I'm
changing it to avoid potential problems in the future.
Assisted-by: Cursor / claude-opus-4.7-thinking-xhigh
