Miscellaneous feature-related build fixes. (#12719)

Most found with cargo-all-features.

Signed-off-by: Piotr Sikora <[email protected]>

Polyfill `ToWasmtimeResult` and add eventually-necessary call sites (#12308)

* Polyfill `ToWasmtimeResult` and add eventually-necessary call sites

This commit polyfills `wasmtime_internal_error::To

Polyfill `ToWasmtimeResult` and add eventually-necessary call sites (#12308)

* Polyfill `ToWasmtimeResult` and add eventually-necessary call sites

This commit polyfills `wasmtime_internal_error::ToWasmtimeResult` in
`wasmtime_environ`, adds the cargo feature plumbing that will eventually connect
to the `"wasmtime_internal_error/anyhow"` cargo feature but for now just
configures this polyfill, and adds uses of the polyfill at all the sites that
will be necessary once we swap out `anyhow` for
`wasmtime_internal_error`. Currently, the polyfill is just an identity function,
because `wasmtime::Result`/`wasmtime_environ::error::Result` is just another
name for `anyhow::Result`. Once we do move away from `anyhow`, however, that
will no longer be the case, and these uses will do the necessary conversion.

My goal with landing this as an incremental commit is to make it so that the
actual commit that does the error crate swap out can be as close to _just_ the
`Cargo.toml` dependency change, without any other code changes as much as
possible. This, in turn, means that swap out should be super easy to revert, if
necessary.

* Add a couple more `.to_wasmtime_result()` invocations in fuzz code

* Revert "Add a couple more `.to_wasmtime_result()` invocations in fuzz code"

This reverts commit b33696e5f63f7eed731ca9dad10fec5e55a550d3.

* Move cranelift fuzz targets back to anyhow

* Fix cargo feature enablement for explorer

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