safe transmute: Rename BikeshedIntrinsicFrom to TransmuteFrom

As our implementation of MCP411 nears completion and we begin to
solicit testing, it's no longer reasonable to expect testers to
type or remember `BikeshedIntrinsicFrom`. The name degrades the
ease-of-reading of documentation, and the overall experience of
using compiler safe transmute.

Tentatively, we'll instead adopt `TransmuteFrom`.

This name seems to be the one most likely to be stabilized, after
discussion on Zulip [1]. We may want to revisit the ordering of
`Src` and `Dst` before stabilization, at which point we'd likely
consider `TransmuteInto` or `Transmute`.

[1] https://rust-lang.zulipchat.com/#narrow/stream/216762-project-safe-transmute/topic/What.20should.20.60BikeshedIntrinsicFrom.60.20be.20named.3F

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -862,7 +862,7 @@ where
         _ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
     ) -> Result<Candidate<I>, NoSolution> {
-        panic!("`BikeshedIntrinsicFrom` does not have an associated type: {:?}", goal)
+        panic!("`TransmuteFrom` does not have an associated type: {:?}", goal)
     }
 
     fn consider_builtin_effects_intersection_candidate(