Deduplicate const-eval fast paths #12243
Description
#12234 introduced a new simple const-eval fast path. We already have one here. We didn't initially share them because the existing one is inside the wasmtime crate and uses wasmtime crate types, which can't be used from inside wasmtime-internal-cranelift. We should resolve this situation by adding traits or moving all of this into wasmtime-environ and adding a WasmValue enum to that crate or something.
Could this also get deduplicated with our preexisting fast path in const-eval?
Originally posted by @alexcrichton in #12234 (comment)