Swich DefIdCache to use LocalDefId for local caching

This should hopefully share monomorphizations with DefIndex, helping
speed up bootstrap time and maybe reduce binary sizes.

Author: Mark-Simulacrum

compiler/rustc_query_system/src/query/caches.rs

@@ -4,7 +4,7 @@ use std::sync::OnceLock;
 
 use rustc_data_structures::sharded::ShardedHashMap;
 pub use rustc_data_structures::vec_cache::VecCache;
-use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_hir::def_id::{LOCAL_CRATE, LocalDefId};
 use rustc_index::Idx;
 use rustc_span::def_id::{DefId, DefIndex};
 
@@ -116,7 +116,7 @@ where
 pub struct DefIdCache<V> {
     /// Stores the local DefIds in a dense map. Local queries are much more often dense, so this is
     /// a win over hashing query keys at marginal memory cost (~5% at most) compared to FxHashMap.
-    local: VecCache<DefIndex, V, DepNodeIndex>,
+    local: VecCache<LocalDefId, V, DepNodeIndex>,
     foreign: DefaultCache<DefId, V>,
 }