Implement simple benchmarks for instantiation.

This adds benchmarks around module instantiation using criterion.

Both the default (i.e. on-demand) and pooling allocators are tested
sequentially and in parallel using a thread pool.

Instantiation is tested with an empty module, a module with a single page
linear memory, a larger linear memory with a data initializer, and a "hello
world" Rust WASI program.

Cargo.lock

@@ -3599,6 +3599,7 @@ name = "wasmtime-cli"
 version = "0.26.0"
 dependencies = [
  "anyhow",
+ "criterion",
  "env_logger 0.8.3",
  "file-per-thread-logger",
  "filecheck",
@@ -3607,6 +3608,7 @@ dependencies = [
  "libc",
  "log",
  "more-asserts",
+ "num_cpus",
  "object",
  "pretty_env_logger",
  "rayon",