Rollup merge of #136279 - Zalathar:ensure-ok, r=oli-obk

Rename `tcx.ensure()` to `tcx.ensure_ok()`, and improve the associated docs

This is all based on my archaeology for https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/.60TyCtxtEnsure.60.

The main renamings are:
- `tcx.ensure()` → `tcx.ensure_ok()`
- `tcx.ensure_with_value()` → `tcx.ensure_done()`
- Query modifier `ensure_forwards_result_if_red` → `return_result_from_ensure_ok`

Hopefully these new names are a better fit for the *actual* function and purpose of these query call modes.

compiler/rustc_ty_utils/src/instance.rs

@@ -225,7 +225,7 @@ fn resolve_associated_item<'tcx>(
             if trait_item_id != leaf_def.item.def_id
                 && let Some(leaf_def_item) = leaf_def.item.def_id.as_local()
             {
-                tcx.ensure().compare_impl_item(leaf_def_item)?;
+                tcx.ensure_ok().compare_impl_item(leaf_def_item)?;
             }
 
             Some(ty::Instance::new(leaf_def.item.def_id, args))