Auto merge of rust-lang#145513 - beepster4096:erasedereftemps, r=saethlin,cjgillot

Validate CopyForDeref and DerefTemps better and remove them from runtime MIR

(split from my WIP rust-lang#145344)

This PR:
- Removes `Rvalue::CopyForDeref` and `LocalInfo::DerefTemp` from runtime MIR
    - Using a new mir pass `EraseDerefTemps`
    - `CopyForDeref(x)` is turned into `Use(Copy(x))`
    - `DerefTemp` is turned into `Boring`
        - Not sure if this part is actually necessary, it made more sense in rust-lang#145344 with `DerefTemp` storing actual data that I wanted to keep from having to be kept in sync with the rest of the body in runtime MIR
- Checks in validation that `CopyForDeref` and `DerefTemp` are only used together
- Removes special handling for `CopyForDeref` from many places
- Removes `CopyForDeref` from `custom_mir` reverting rust-lang#111587
    - In runtime MIR simple copies can be used instead
    - In post cleanup analysis MIR it was already wrong to use due to the lack of support for creating `DerefTemp` locals
    - Possibly this should be its own PR?
 - Adds an argument to `deref_finder` to avoid creating new `DerefTemp`s and `CopyForDeref` in runtime MIR.
     - Ideally we would just avoid making intermediate derefs instead of fixing it at the end of a pass / during shim building
 - Removes some usages of `deref_finder` that I found out don't actually do anything

r? oli-obk

Author: bors

core/src/intrinsics/mir.rs

@@ -233,7 +233,7 @@
 //!
 //!  - Operands implicitly convert to `Use` rvalues.
 //!  - `&`, `&mut`, `addr_of!`, and `addr_of_mut!` all work to create their associated rvalue.
-//!  - [`CopyForDeref`], [`CastTransmute`], [`CastPtrToPtr`], [`CastUnsize`], and [`Discriminant`]
+//!  - [`CastTransmute`], [`CastPtrToPtr`], [`CastUnsize`], and [`Discriminant`]
 //!    have associated functions.
 //!  - Unary and binary operations use their normal Rust syntax - `a * b`, `!c`, etc.
 //!  - The binary operation `Offset` can be created via [`Offset`].
@@ -405,7 +405,6 @@ define!(
     "mir_ptr_metadata",
     fn PtrMetadata<P: ?Sized>(place: *const P) -> <P as ::core::ptr::Pointee>::Metadata
 );
-define!("mir_copy_for_deref", fn CopyForDeref<T>(place: T) -> T);
 define!("mir_retag", fn Retag<T>(place: T));
 define!("mir_move", fn Move<T>(place: T) -> T);
 define!("mir_static", fn Static<T>(s: T) -> &'static T);