Remaining excess recompilation

### General summary/comments (optional)

Following resolution of #3732, there is still some unnecessary recompilation going on in some situations, as noted in the PR #3750. Not sure if this will be resolved by per component builds, or whether it should be attacked in the meantime, so I thought I'd note it in this issue. It seems to me the solution will require some reworking of `constructPlan`. I'm happy to take a look at it but if you think it's more appropriate for somebody else that's fine too!

### Steps to reproduce

Have a project with 2 packages where `bar` depends on `foo`. Compile `foo` with tests (e.g. `stack build foo:foo-test bar`). Edit a `foo` test module is edited `bar` will be unregistered and recompiled.

### Expected

`foo`'s test suite is recompiled but no action for `bar` is necessary.

### Actual

`bar` will also be unregistered and recompiled, despite the fact that none of the code that it depends on changed.

### Stack version

Local build of branch for the fix for #3732.