Since wasmer 0.17 no backends are enabled by default. Backends are now detected
using the [makefile](https://github.com/wasmerio/wasmer/blob/master/Makefile).
This change enables cranelift as this used to be the old default. At
least one backend is needed for the `run` subcommand to work. If we want
to replicate the actual logic in the makefile, we would probably want to
enable the singlepass and llvm backend as well. However enabling llvm
backend introduces a dependency on openssl, so we opted for replicating
the old default behavior.
Changes the default fetcher in the Rust Platform to be the newer
`fetchCargoTarball`, and changes every application using the current default to
instead opt out.
This commit does not change any hashes or cause any rebuilds. Once integrated,
we will start deleting the opt-outs and recomputing hashes.
See #79975 for details.
