Enable jitdump profiling support by default (#1310)

* Enable jitdump profiling support by default

This the result of some of the investigation I was doing for #1017. I've
done a number of refactorings here which culminated in a number of
changes that all amount to what I think should result in jitdump support being
enabled by default:

* Pass in a list of finished functions instead of just a range to
  ensure that we're emitting jit dump data for a specific module rather
  than a whole `CodeMemory` which may have other modules.
* Define `ProfilingStrategy` in the `wasmtime` crate to have everything
  locally-defined
* Add support to the C API to enable profiling
* Documentation added for profiling with jitdump to the book
* Split out supported/unsupported files in `jitdump.rs` to avoid having
  lots of `#[cfg]`.
* Make dependencies optional that are only used for `jitdump`.
* Move initialization up-front to `JitDumpAgent::new()` instead of
  deferring it to the first module.
* Pass around `Arc<dyn ProfilingAgent>` instead of
  `Option<Arc<Mutex<Box<dyn ProfilingAgent>>>>`

The `jitdump` Cargo feature is now enabled by default which means that
our published binaries, C API artifacts, and crates will support
profiling at runtime by default. The support I don't think is fully
fleshed out and working but I think it's probably in a good enough spot
we can get users playing around with it!

src/lib.rs

@@ -30,8 +30,7 @@ mod obj;
 use anyhow::{bail, Result};
 use std::path::PathBuf;
 use structopt::StructOpt;
-use wasmtime::{Config, Strategy};
-use wasmtime_profiling::ProfilingStrategy;
+use wasmtime::{Config, ProfilingStrategy, Strategy};
 
 pub use obj::compile_to_obj;
 
@@ -46,8 +45,8 @@ fn pick_compilation_strategy(cranelift: bool, lightbeam: bool) -> Result<Strateg
 
 fn pick_profiling_strategy(jitdump: bool) -> Result<ProfilingStrategy> {
     Ok(match jitdump {
-        true => ProfilingStrategy::JitDumpProfiler,
-        false => ProfilingStrategy::NullProfiler,
+        true => ProfilingStrategy::JitDump,
+        false => ProfilingStrategy::None,
     })
 }