Use Cargo's "namespace features" feature (#4293)

Cargo recently added the ability to have an optional dependency without
implicitly introducing a new named feature on a crate. This is triggered
with some new directives in the `[features]` section, specifically:

* The `dep:foo` syntax means that `foo` is activated but no implicit
  feature should be added named `foo`.

* Additionally `foo?/bar` means that the `bar` feature of `foo` is only
  activated if `foo` is otherwise activated elsewhere, for example a
  conditional activation.

These two features can help avoid extra feature names showing up that we
don't want (e.g. currently the `wasmtime` crate has a `rayon` feature)
and additionally can help avoid runtime dependencies in niche cases for
us (e.g. activating `all-arch` but disabling `cranelift` would
previously pull-in cranelift but no longer will).

Cargo.toml

@@ -101,8 +101,8 @@ default = [
 ]
 jitdump = ["wasmtime/jitdump"]
 vtune = ["wasmtime/vtune"]
-wasi-crypto = ["wasmtime-wasi-crypto"]
-wasi-nn = ["wasmtime-wasi-nn"]
+wasi-crypto = ["dep:wasmtime-wasi-crypto"]
+wasi-nn = ["dep:wasmtime-wasi-nn"]
 memory-init-cow = ["wasmtime/memory-init-cow", "wasmtime-cli-flags/memory-init-cow"]
 pooling-allocator = ["wasmtime/pooling-allocator", "wasmtime-cli-flags/pooling-allocator"]
 all-arch = ["wasmtime/all-arch"]

crates/wasmtime/Cargo.toml

@@ -67,7 +67,7 @@ default = [
 # with the Cranelift compiler. Cranelift is the default compilation backend of
 # Wasmtime. If disabled then WebAssembly modules can only be created from
 # precompiled WebAssembly modules.
-cranelift = ["wasmtime-cranelift"]
+cranelift = ["dep:wasmtime-cranelift"]
 
 # Enables support for the `perf` jitdump profiler
 jitdump = ["wasmtime-jit/jitdump"]
@@ -76,22 +76,22 @@ jitdump = ["wasmtime-jit/jitdump"]
 vtune = ["wasmtime-jit/vtune"]
 
 # Enables parallel compilation of WebAssembly code.
-parallel-compilation = ["rayon"]
+parallel-compilation = ["dep:rayon"]
 
 # Enables support for automatic cache configuration to be enabled in `Config`.
-cache = ["wasmtime-cache"]
+cache = ["dep:wasmtime-cache"]
 
 # Enables support for "async stores" as well as defining host functions as
 # `async fn` and calling functions asynchronously.
-async = ["wasmtime-fiber", "wasmtime-runtime/async", "async-trait"]
+async = ["dep:wasmtime-fiber", "wasmtime-runtime/async", "dep:async-trait"]
 
 # Enables support for the pooling instance allocation strategy
 pooling-allocator = ["wasmtime-runtime/pooling-allocator"]
 
 # Enables support for all architectures in Cranelift, allowing
 # cross-compilation using the `wasmtime` crate's API, notably the
 # `Engine::precompile_module` function.
-all-arch = ["wasmtime-cranelift/all-arch"]
+all-arch = ["wasmtime-cranelift?/all-arch"]
 
 # Enables trap handling using POSIX signals instead of Mach exceptions on MacOS.
 # It is useful for applications that do not bind their own exception ports and