Rollup merge of #125750 - compiler-errors:expect, r=lcnr

Align `Term` methods with `GenericArg` methods, add `Term::expect_*`

* `Term::ty` -> `Term::as_type`.
* `Term::ct` -> `Term::as_const`.
* Adds `Term::expect_type` and `Term::expect_const`, and uses them in favor of `.ty().unwrap()`, etc.

I could also shorten these to `as_ty` and then do `GenericArg::as_ty` as well, but I do think the `as_` is important to signal that this is a conversion method, and not a getter, like `Const::ty` is.

r? types

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -263,7 +263,7 @@ fn push_debuginfo_type_name<'tcx>(
                         let ExistentialProjection { def_id: item_def_id, term, .. } =
                             tcx.instantiate_bound_regions_with_erased(bound);
                         // FIXME(associated_const_equality): allow for consts here
-                        (item_def_id, term.ty().unwrap())
+                        (item_def_id, term.expect_type())
                     })
                     .collect();