Rollup merge of #143140 - RalfJung:ptr-into-parts, r=oli-obk

give Pointer::into_parts a more scary name and offer a safer alternative

`into_parts` is a bit too innocent of a name for a somewhat subtle operation.
r? `@oli-obk`

compiler/rustc_codegen_gcc/src/common.rs

@@ -248,7 +248,7 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                 }
             }
             Scalar::Ptr(ptr, _size) => {
-                let (prov, offset) = ptr.into_parts(); // we know the `offset` is relative
+                let (prov, offset) = ptr.prov_and_relative_offset();
                 let alloc_id = prov.alloc_id();
                 let base_addr = match self.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {