Auto merge of #100726 - jswrenn:transmute, r=oli-obk

safe transmute: use `Assume` struct to provide analysis options

This task was left as a TODO in #92268; resolving it brings [`BikeshedIntrinsicFrom`](https://doc.rust-lang.org/nightly/core/mem/trait.BikeshedIntrinsicFrom.html) more in line with the API defined in [MCP411](https://github.com/rust-lang/compiler-team/issues/411).

**Before:**
```rust
pub unsafe trait BikeshedIntrinsicFrom<
    Src,
    Context,
    const ASSUME_ALIGNMENT: bool,
    const ASSUME_LIFETIMES: bool,
    const ASSUME_VALIDITY: bool,
    const ASSUME_VISIBILITY: bool,
> where
    Src: ?Sized,
{}
```
**After:**
```rust
pub unsafe trait BikeshedIntrinsicFrom<Src, Context, const ASSUME: Assume = { Assume::NOTHING }>
where
    Src: ?Sized,
{}
```

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

r? `@oli-obk`

---

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

compiler/rustc_span/src/symbol.rs

@@ -339,6 +339,7 @@ symbols! {
         alias,
         align,
         align_offset,
+        alignment,
         alignstack,
         all,
         alloc,
@@ -866,6 +867,7 @@ symbols! {
         lib,
         libc,
         lifetime,
+        lifetimes,
         likely,
         line,
         line_macro,
@@ -1294,6 +1296,7 @@ symbols! {
         rustfmt,
         rvalue_static_promotion,
         s,
+        safety,
         sanitize,
         sanitizer_runtime,
         saturating_add,
@@ -1478,6 +1481,7 @@ symbols! {
         trait_alias,
         trait_upcasting,
         transmute,
+        transmute_opts,
         transmute_trait,
         transparent,
         transparent_enums,
@@ -1573,6 +1577,7 @@ symbols! {
         va_list,
         va_start,
         val,
+        validity,
         values,
         var,
         variant_count,