10387: Move `IdxRange` into la-arena r=Veykril a=arzg
Currently, `IdxRange` (named `IdRange`) is located in `hir_def::item_tree`, when really it isn’t specific to `hir_def` and could become part of la-arena. The rename from `IdRange` to `IdxRange` is to maintain consistency with the naming convention used throughout la-arena (`Idx` instead of `Id`, `RawIdx` instead of `RawId`). This PR also adds a few new APIs to la-arena on top of `IdxRange` for convenience, namely:
- indexing into an `Arena` by an `IdxRange` and getting a slice of values back
- creating an `IdxRange` from an inclusive range
Currently this PR also exposes a new `Arena::next_idx` method to make constructing inclusive`IdxRange`s using `IdxRange::new` easier; however, it would in my opinion be better to remove this as it allows for easy creation of out-of-bounds `Idx`s, when `IdxRange::new_inclusive` mostly covers the same use-case while being less error-prone.
I decided to bump the la-arena version to 0.3.0 from 0.2.0 because adding a new `Index` impl for `Arena` turned out to be a breaking change: I had to add a type hint in `crates/hir_def/src/body/scope.rs` when one wasn’t necessary before, since rustc couldn’t work out the type of a closure parameter now that there are multiple `Index` impls. I’m not sure whether this is the right decision, though.
Co-authored-by: Aramis Razzaghipour <aramisnoah@gmail.com>
