internal: Use ItemTree for variant, field and module attribute collection in attrs_query

[Veykril]

Less parsing = very good, should speed up lang item collection as that basically probes attributes of all enum variants which currently triggers parsing

Not fond of how this is searching for the correct index, ideally we'd map between HIR and item tree Id here but I am not sure how, storing the item tree ids in the HIR version doesn't work due to the usage of Trace...

[Veykril]

So usually we fetch the item tree index via Lookup::lookup fetching the *Loc data, we don't have that for variants or fields, so the question is, would it make sense adding these? It sounds like that would increase memory usage by a good bit potentially so I'm not sure. Similarly it would be beneficial for us to be able to fetch the item tree id of a module, that way we can basically skip parsing for modules in attr_query altogether (except for Blockexpr modules but those are rare anyways)

[Veykril]

@bors r+

[bors]

📌 Commit 0081ef3 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0081ef3 with merge d469e0d...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing d469e0d to master...