generate precise traps in fused component adapters

[dicej]

As of this writing, the fused adapter compiler in wasmtime-environ generates unreachable instructions to trap in various scenarios, e.g. when a component instance tries to call an import when that is disallowed. It also generates metadata to record the precise reason for the trap and stores that in fact::trampoline::Compiler::traps. However, that metadata isn't used anywhere, so at runtime the user always sees the generic "wasm `unreachable` instruction executed" message; the precise reason is no longer available. Consequently, we've had to temporarily fork a few spec tests which expect precise trap messages, replacing them with generic ones.