Update const_conditions and explicit_implied_const_bounds docs

Move documentation to query definitions, and add docs to
`explicit_implied_const_bounds`.

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -940,12 +940,6 @@ impl<'tcx> ItemCtxt<'tcx> {
     }
 }
 
-/// Compute the conditions that need to hold for a conditionally-const item to be const.
-/// That is, compute the set of `~const` where clauses for a given item.
-///
-/// This query also computes the `~const` where clauses for associated types, which are
-/// not "const", but which have item bounds which may be `~const`. These must hold for
-/// the `~const` item bound to hold.
 pub(super) fn const_conditions<'tcx>(
     tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
@@ -1063,7 +1057,9 @@ pub(super) fn explicit_implied_const_bounds<'tcx>(
     def_id: LocalDefId,
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::PolyTraitRef<'tcx>, Span)]> {
     if !tcx.is_conditionally_const(def_id) {
-        bug!("const_conditions invoked for item that is not conditionally const: {def_id:?}");
+        bug!(
+            "explicit_implied_const_bounds invoked for item that is not conditionally const: {def_id:?}"
+        );
     }
 
     let bounds = match tcx.opt_rpitit_info(def_id.to_def_id()) {

compiler/rustc_middle/src/query/mod.rs

@@ -748,6 +748,15 @@ rustc_queries! {
         }
     }
 
+    /// Compute the conditions that need to hold for a conditionally-const item to be const.
+    /// That is, compute the set of `~const` where clauses for a given item.
+    ///
+    /// This can be thought of as the `~const` equivalent of `predicates_of`. These are the
+    /// predicates that need to be proven at usage sites, and can be assumed at definition.
+    ///
+    /// This query also computes the `~const` where clauses for associated types, which are
+    /// not "const", but which have item bounds which may be `~const`. These must hold for
+    /// the `~const` item bound to hold.
     query const_conditions(
         key: DefId
     ) -> ty::ConstConditions<'tcx> {
@@ -757,6 +766,11 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Compute the const bounds that are implied for a conditionally-const item.
+    ///
+    /// This can be though of as the `~const` equivalent of `explicit_item_bounds`. These
+    /// are the predicates that need to proven at definition sites, and can be assumed at
+    /// usage sites.
     query explicit_implied_const_bounds(
         key: DefId
     ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::PolyTraitRef<'tcx>, Span)]> {