Change `HandleNameAsExpr()` to to generate the `InstId` before calling `LookupUnqualifiedName()`

[bricknerb]

trafficstars

This is a test to show the impact such a change has before we require to have InstId instead of LocId for marking the poisoning location.

See related discussion https://discord.com/channels/655572317891461132/655578254970716160/1353756101409243146