Rollup merge of #40518 - michaelwoerister:hir-id, r=eddyb

Introduce HirId, a replacement for ast::NodeId after lowering to HIR

This is the first step towards implementing #40303. This PR introduces the `HirId` type and generates a `HirId` for everything that would be assigned one (i.e. stuff in the HIR), but the HIR data types still use `NodeId` for now. Changing that is a big refactoring that I want to do in a separate PR.

A `HirId` uniquely identifies a node in the HIR of the current crate. It is composed of the `owner`, which is the `DefIndex` of the directly enclosing `hir::Item`, `hir::TraitItem`, or `hir::ImplItem` (i.e. the closest "item-like"), and the `local_id` which is unique within the given owner.

This PR is also running a number of consistency checks for the generated `HirId`s:
- Does `NodeId` in the HIR have a corresponding `HirId`?
- Is the `owner` part of each `HirId` consistent with its position in the HIR?
- Do the numerical values of the `local_id` part all lie within a dense range of integers?

cc @rust-lang/compiler

r? @eddyb or @nikomatsakis

src/test/compile-fail/region-bounds-on-objects-and-type-parameters.rs

@@ -18,7 +18,7 @@ trait SomeTrait { }
 
 // Bounds on object types:
 
-struct Foo<'a,'b,'c> { //~ ERROR parameter `'b` is never used
+struct Foo<'a,'b,'c> { //~ ERROR parameter `'c` is never used
     // All of these are ok, because we can derive exactly one bound:
     a: Box<IsStatic>,
     b: Box<Is<'static>>,