Auto merge of #107055 - kylematsuda:eb-fn-sig, r=lcnr

Switch to `EarlyBinder` for `fn_sig` query

Part of the work to finish #105779 (also see rust-lang/types-team#78).

Several queries `X` have a `bound_X` variant that wraps the output in [`EarlyBinder`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/subst/struct.EarlyBinder.html). This adds `EarlyBinder` to the return type of the `fn_sig` query and removes `bound_fn_sig`.

r? `@lcnr`

Author: bors

src/eval.rs

@@ -357,7 +357,7 @@ pub fn create_ecx<'mir, 'tcx: 'mir>(
     match entry_type {
         EntryFnType::Main { .. } => {
             let start_id = tcx.lang_items().start_fn().unwrap();
-            let main_ret_ty = tcx.fn_sig(entry_id).output();
+            let main_ret_ty = tcx.fn_sig(entry_id).no_bound_vars().unwrap().output();
             let main_ret_ty = main_ret_ty.no_bound_vars().unwrap();
             let start_instance = ty::Instance::resolve(
                 tcx,