refactor: Lower type-refs before type inference

This refactors how we deal with items in hir-def lowering.

- It now lowers all of them through an "ExpressionStore" (kind of a misnomer as this point) as their so called *Signatures.
- We now uniformly lower type AST into TypeRefs before type inference.
- Likewise, this moves macro expansion out of type inference, resulting in a single place where we do non-defmap macro expansion.
- Finally, this PR removes a lot of information from ItemTree, making the DefMap a lot less likely to be recomputed and have it only depend on actual early name resolution related information (not 100% true, we still have ADT fields in there but thats a follow up removal).

Author: Veykril

src/tools/rust-analyzer/crates/hir-def/src/attr.rs

@@ -76,7 +76,6 @@ impl Attrs {
         let _p = tracing::info_span!("fields_attrs_query").entered();
         // FIXME: There should be some proper form of mapping between item tree field ids and hir field ids
         let mut res = ArenaMap::default();
-
         let item_tree;
         let (parent, fields, krate) = match v {
             VariantId::EnumVariantId(it) => {