compiler: Use size_of from the prelude instead of imported

Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.

These functions were added to all preludes in Rust 1.80.

compiler/rustc_resolve/src/late.rs

@@ -2994,7 +2994,7 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     }
 
     // HACK(min_const_generics, generic_const_exprs): We
-    // want to keep allowing `[0; std::mem::size_of::<*mut T>()]`
+    // want to keep allowing `[0; size_of::<*mut T>()]`
     // with a future compat lint for now. We do this by adding an
     // additional special case for repeat expressions.
     //