rustc_hir_analysis: add a helper to check function the signature mismatches

This function is now used to check `#[panic_handler]`, `start` lang item, `main`, `#[start]` and intrinsic functions.

The diagnosis produced are now closer to the ones produced by trait/impl method signature mismatch.

compiler/rustc_infer/src/errors/mod.rs

@@ -1463,6 +1463,14 @@ pub enum ObligationCauseFailureCode {
         #[subdiagnostic]
         subdiags: Vec<TypeErrorAdditionalDiags>,
     },
+    #[diag(infer_oc_fn_lang_correct_type, code = "E0308")]
+    FnLangCorrectType {
+        #[primary_span]
+        span: Span,
+        #[subdiagnostic]
+        subdiags: Vec<TypeErrorAdditionalDiags>,
+        lang_item_name: Symbol,
+    },
     #[diag(infer_oc_intrinsic_correct_type, code = "E0308")]
     IntrinsicCorrectType {
         #[primary_span]