Auto merge of #95826 - carbotaniuman:miri-permissive-provenance, r=RalfJung

Initial work on Miri permissive-exposed-provenance

Rustc portion of the changes for portions of a permissive ptr-to-int model for Miri. The main changes here are changing `ptr_get_alloc` and `get_alloc_id` to return an Option, and also making ptr-to-int casts have an expose side effect.

src/test/ui/consts/miri_unleashed/ptr_arith.rs

@@ -14,7 +14,7 @@ static CMP: () = {
 static PTR_INT_CAST: () = {
     let x = &0 as *const _ as usize;
     //~^ ERROR could not evaluate static initializer
-    //~| unable to turn pointer into raw bytes
+    //~| "exposing pointers" needs an rfc before being allowed inside constants
     let _v = x == x;
 };
 

src/test/ui/consts/miri_unleashed/ptr_arith.stderr

@@ -8,7 +8,7 @@ error[E0080]: could not evaluate static initializer
   --> $DIR/ptr_arith.rs:15:13
    |
 LL |     let x = &0 as *const _ as usize;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^ unable to turn pointer into raw bytes
+   |             ^^^^^^^^^^^^^^^^^^^^^^^ "exposing pointers" needs an rfc before being allowed inside constants
 
 error[E0080]: could not evaluate static initializer
   --> $DIR/ptr_arith.rs:23:14