Rollup merge of #104357 - RalfJung:is-sized, r=cjgillot

add is_sized method on Abi and Layout, and use it

This avoids the double negation of `!is_unsized()` that we have quite a lot.

compiler/rustc_codegen_llvm/src/debuginfo/utils.rs

@@ -72,7 +72,7 @@ pub(crate) fn fat_pointer_kind<'ll, 'tcx>(
         layout.is_unsized()
     );
 
-    if !layout.is_unsized() {
+    if layout.is_sized() {
         return None;
     }
 

compiler/rustc_codegen_llvm/src/type_of.rs

@@ -140,7 +140,7 @@ fn struct_llfields<'a, 'tcx>(
         prev_effective_align = effective_field_align;
     }
     let padding_used = result.len() > field_count;
-    if !layout.is_unsized() && field_count > 0 {
+    if layout.is_sized() && field_count > 0 {
         if offset > layout.size {
             bug!("layout: {:#?} stride: {:?} offset: {:?}", layout, layout.size, offset);
         }