Auto merge of #99013 - RalfJung:dont-poison-my-places, r=oli-obk

interpret: get rid of MemPlaceMeta::Poison

This is achieved by refactoring the projection code (`{mplace,place,operand}_{downcast,field,index,...}`) so that we no longer need to call `assert_mem_place` in the operand handling.

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -225,6 +225,8 @@ impl<Tag> Allocation<Tag> {
 
     /// Try to create an Allocation of `size` bytes, failing if there is not enough memory
     /// available to the compiler to do so.
+    ///
+    /// If `panic_on_fail` is true, this will never return `Err`.
     pub fn uninit<'tcx>(size: Size, align: Align, panic_on_fail: bool) -> InterpResult<'tcx, Self> {
         let bytes = Box::<[u8]>::try_new_zeroed_slice(size.bytes_usize()).map_err(|_| {
             // This results in an error that can happen non-deterministically, since the memory