Rollup merge of #112810 - compiler-errors:dont-ice-on-bad-layout, r=wesleywiser

Don't ICE on unnormalized struct tail in layout computation

1. We try to compute a `SizeSkeleton` even if a layout error occurs, but we really only need to do this if we get `LayoutError::Unknown`, since that means our type is too polymorphic to actually compute the full layout. If we have other errors, like `LayoutError::NormalizationError` or `LayoutError::Cycle`, then we can't really make any progress, since this represents an actual error.
2. Avoid using `normalize_erasing_regions` and `struct_tail_erasing_lifetimes` since those ICE on normalization errors, and since we may call `layout_of` in HIR typeck, we don't know for certain that we're on the happy path.

Fixes #112736

compiler/rustc_middle/src/ty/layout.rs

@@ -318,7 +318,13 @@ impl<'tcx> SizeSkeleton<'tcx> {
             Ok(layout) => {
                 return Ok(SizeSkeleton::Known(layout.size));
             }
-            Err(err) => err,
+            Err(err @ LayoutError::Unknown(_)) => err,
+            // We can't extract SizeSkeleton info from other layout errors
+            Err(
+                e @ LayoutError::Cycle
+                | e @ LayoutError::SizeOverflow(_)
+                | e @ LayoutError::NormalizationFailure(..),
+            ) => return Err(e),
         };
 
         match *ty.kind() {