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

compiler/rustc_span/src/symbol.rs

@@ -334,6 +334,7 @@ symbols! {
         alias,
         align,
         align_offset,
+        alignment,
         alignstack,
         all,
         alloc,
@@ -859,6 +860,7 @@ symbols! {
         lib,
         libc,
         lifetime,
+        lifetimes,
         likely,
         line,
         line_macro,
@@ -1284,6 +1286,7 @@ symbols! {
         rustfmt,
         rvalue_static_promotion,
         s,
+        safety,
         sanitize,
         sanitizer_runtime,
         saturating_add,
@@ -1466,6 +1469,7 @@ symbols! {
         trait_alias,
         trait_upcasting,
         transmute,
+        transmute_opts,
         transmute_trait,
         transparent,
         transparent_enums,
@@ -1560,6 +1564,7 @@ symbols! {
         va_list,
         va_start,
         val,
+        validity,
         values,
         var,
         variant_count,