Rollup merge of #121146 - compiler-errors:ignore-diverging-arms, r=estebank

Only point out non-diverging arms for match suggestions

Fixes #121144

There is no reason to point at diverging arms, which will always coerce to whatever is the match block's evaluated type.

This also removes the suggestion from #106601, since as I pointed out in https://github.com/rust-lang/rust/issues/72634#issuecomment-1946210898 the added suggestion is not firing in the right cases, but instead only when one of the match arms already *actually* evaluates to `()`.

r? estebank

compiler/rustc_middle/src/traits/mod.rs

@@ -569,9 +569,8 @@ pub struct MatchExpressionArmCause<'tcx> {
     pub prior_arm_ty: Ty<'tcx>,
     pub prior_arm_span: Span,
     pub scrut_span: Span,
-    pub scrut_hir_id: hir::HirId,
     pub source: hir::MatchSource,
-    pub prior_arms: Vec<Span>,
+    pub prior_non_diverging_arms: Vec<Span>,
     pub opt_suggest_box_span: Option<Span>,
 }