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_resolve/src/late.rs

@@ -300,7 +300,7 @@ impl<'a> PathSource<'a> {
                 Res::Def(
                     DefKind::Ctor(_, CtorKind::Const | CtorKind::Fn)
                         | DefKind::Const
-                        | DefKind::Static
+                        | DefKind::Static(_)
                         | DefKind::Fn
                         | DefKind::AssocFn
                         | DefKind::AssocConst
@@ -1830,7 +1830,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 }
                 Some(res)
             }
-            Res::Def(DefKind::Ctor(..) | DefKind::Const | DefKind::Static, _) => {
+            Res::Def(DefKind::Ctor(..) | DefKind::Const | DefKind::Static(_), _) => {
                 // This is unambiguously a fresh binding, either syntactically
                 // (e.g., `IDENT @ PAT` or `ref IDENT`) or because `IDENT` resolves
                 // to something unusable as a pattern (e.g., constructor function),