Rename HandlerInner::delay_span_bug as HandlerInner::span_delayed_bug.

Because the corresponding `Level` is `DelayedBug` and `span_delayed_bug`
follows the pattern used everywhere else: `span_err`, `span_warning`,
etc.

compiler/rustc_span/src/lib.rs

@@ -2247,7 +2247,7 @@ pub struct ErrorGuaranteed(());
 impl ErrorGuaranteed {
     /// To be used only if you really know what you are doing... ideally, we would find a way to
     /// eliminate all calls to this method.
-    #[deprecated = "`Session::delay_span_bug` should be preferred over this function"]
+    #[deprecated = "`Session::span_delayed_bug` should be preferred over this function"]
     pub fn unchecked_claim_error_was_emitted() -> Self {
         ErrorGuaranteed(())
     }