safe transmute: use Assume struct to provide analysis options

This was left as a TODO in #92268, and brings the trait more in
line with what was defined in MCP411.

`Assume::visibility` has been renamed to `Assume::safety`, as
library safety is what's actually being assumed; visibility is
just the mechanism by which it is currently checked (this may
change).

ref: https://github.com/rust-lang/compiler-team/issues/411
ref: https://github.com/rust-lang/rust/issues/99571

library/core/src/lib.rs

@@ -93,6 +93,7 @@
 #![warn(missing_debug_implementations)]
 #![warn(missing_docs)]
 #![allow(explicit_outlives_requirements)]
+#![allow(incomplete_features)]
 //
 // Library features:
 #![feature(const_align_offset)]
@@ -160,6 +161,7 @@
 //
 // Language features:
 #![feature(abi_unadjusted)]
+#![feature(adt_const_params)]
 #![feature(allow_internal_unsafe)]
 #![feature(allow_internal_unstable)]
 #![feature(associated_type_bounds)]