Auto merge of #97019 - b-naber:transition-to-valtrees-pt1, r=oli-obk

Transition to valtrees pt1

Compartmentalising https://github.com/rust-lang/rust/pull/96591 as much as possible.

r? `@oli-obk`

compiler/rustc_const_eval/src/interpret/place.rs

@@ -115,12 +115,6 @@ impl<'tcx, Tag: Provenance> std::ops::Deref for MPlaceTy<'tcx, Tag> {
     }
 }
 
-impl<'tcx, Tag: Provenance> std::ops::DerefMut for MPlaceTy<'tcx, Tag> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.mplace
-    }
-}
-
 impl<'tcx, Tag: Provenance> From<MPlaceTy<'tcx, Tag>> for PlaceTy<'tcx, Tag> {
     #[inline(always)]
     fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
@@ -196,6 +190,18 @@ impl<'tcx, Tag: Provenance> MPlaceTy<'tcx, Tag> {
         MPlaceTy { mplace: MemPlace::from_ptr(ptr, layout.align.abi), layout }
     }
 
+    #[inline]
+    pub fn from_aligned_ptr_with_meta(
+        ptr: Pointer<Option<Tag>>,
+        layout: TyAndLayout<'tcx>,
+        meta: MemPlaceMeta<Tag>,
+    ) -> Self {
+        let mut mplace = MemPlace::from_ptr(ptr, layout.align.abi);
+        mplace.meta = meta;
+
+        MPlaceTy { mplace, layout }
+    }
+
     #[inline]
     pub(crate) fn len(&self, cx: &impl HasDataLayout) -> InterpResult<'tcx, u64> {
         if self.layout.is_unsized() {
@@ -495,7 +501,7 @@ where
 
     /// Project into an mplace
     #[instrument(skip(self), level = "debug")]
-    pub(crate) fn mplace_projection(
+    pub(super) fn mplace_projection(
         &self,
         base: &MPlaceTy<'tcx, M::PointerTag>,
         proj_elem: mir::PlaceElem<'tcx>,