Auto merge of #103877 - oli-obk:const_eval_step_limit, r=fee1-dead

Replace const eval limit by a lint and add an exponential backoff warning

The lint triggers at the first power of 2 that comes after 1 million function calls or traversed back-edges (takes less than a second on usual programs). After the first emission, an unsilenceable warning is repeated at every following power of 2 terminators, causing it to get reported less and less the longer the evaluation runs.

cc `@rust-lang/wg-const-eval`

fixes #93481
closes #67217

compiler/rustc_session/src/session.rs

@@ -128,8 +128,6 @@ pub struct Limits {
     pub move_size_limit: Limit,
     /// The maximum length of types during monomorphization.
     pub type_length_limit: Limit,
-    /// The maximum blocks a const expression can evaluate.
-    pub const_eval_limit: Limit,
 }
 
 pub struct CompilerIO {