go/types, types2: gopls crash in recordTypeAndValue [1.18 backport]

[gopherbot]

@findleyr requested issue #51658 to be considered for backport to the next 1.18 minor release.

@gopherbot please backport this to 1.18, it's a deterministic panic.

[gopherbot]

Change https://go.dev/cl/392577 mentions this issue: [release-branch.go1.18] go/types, types2: use correct underlying type in union set computation

[toothrot]

Approved. This is a serious issue with no workaround.

[gopherbot]

Closed by merging 9d73848 to release-branch.go1.18.