Reduce number of crates needed for Config usage

This commit is an attempt to reduce the number of crates necessary to
link to when using `wasmtime::Config` in "default mode" or with only one
or two tweaks. The change moves to a builder-style pattern for `Config`
to only require importing crates as necessary if you configure a
particular setting. This then also propagates that change to `Context`
as well by taking a `Config` instead of requiring that all arguments are
passed alone.

crates/misc/rust/Cargo.toml

@@ -15,8 +15,6 @@ test = false
 doctest = false
 
 [dependencies]
-cranelift-codegen = "0.50.0"
-cranelift-native = "0.50.0"
 wasmtime-interface-types = { path = "../../interface-types" }
 wasmtime-jit = { path = "../../jit" }
 wasmtime-rust-macro = { path = "./macro" }