Extract overlap_check_considering_specialization from insert

[spastorino]

I think this or something along the lines the proposed changes is a bit simpler to read. Also I'm starting to work on #102678 and I don't want to keep mutating the insert method :).

r? @compiler-errors

[compiler-errors]

I'm not sure if I understand the motivation for this refactor. Are you using overlap_check_considering_specialization somewhere else? I'd prefer if you stacked this commit into some other PR where it's actually being used.

[compiler-errors]

"Inserted" makes no sense anymore, because we're not inserting anything until after this fn returns.

[spastorino]

I've renamed Inserted to OverlapResult and changed all the variant names. I think it makes a bit more sense now but maybe still improvable.

[spastorino]

I'm not sure if I understand the motivation for this refactor. Are you using overlap_check_considering_specialization somewhere else? I'd prefer if you stacked this commit into some other PR where it's actually being used.

It's just to extract code that exist to do overlap check and specialization checks that lives inline inside insert. My plan was to land this first and then open a new PR to change how coherence overlap check works to fix #102678.

Anyway, we can land everything in one bigger PR if you prefer.

[compiler-errors]

Let's wait until the follow-up PR that actually uses this.