Remember mutability in DefKind::Static.

This allows to compute the `BodyOwnerKind` from `DefKind` only, and
removes a direct dependency of some MIR queries onto HIR.

As a side effect, it also simplifies metadata, since we don't need 4
flavours of `EntryKind::*Static` any more.

compiler/rustc_monomorphize/src/polymorphize.rs

@@ -158,7 +158,7 @@ fn mark_used_by_default_parameters<'tcx>(
         | DefKind::Fn
         | DefKind::Const
         | DefKind::ConstParam
-        | DefKind::Static
+        | DefKind::Static(_)
         | DefKind::Ctor(_, _)
         | DefKind::AssocFn
         | DefKind::AssocConst