Remove const eval limit and implement an exponential backoff lint instead

Author: oli-obk

crates/hir-def/src/builtin_attr.rs

@@ -195,10 +195,6 @@ pub const INERT_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Limits:
     ungated!(recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
     ungated!(type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing),
-    gated!(
-        const_eval_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
-        const_eval_limit, experimental!(const_eval_limit)
-    ),
     gated!(
         move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
         large_assignments, experimental!(move_size_limit)