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!

crates/jit/src/compiler.rs

@@ -22,7 +22,6 @@ use wasmtime_environ::{
     FunctionBodyData, Module, ModuleMemoryOffset, ModuleVmctxInfo, Relocation, Relocations, Traps,
     Tunables, VMOffsets,
 };
-use wasmtime_profiling::ProfilingAgent;
 use wasmtime_runtime::{
     InstantiationError, SignatureRegistry, TrapRegistration, TrapRegistry, VMFunctionBody,
     VMSharedSignatureIndex, VMTrampoline,
@@ -246,16 +245,6 @@ impl Compiler {
         self.code_memory.publish();
     }
 
-    pub(crate) fn profiler_module_load(
-        &mut self,
-        profiler: &mut Box<dyn ProfilingAgent + Send>,
-        module_name: &str,
-        dbg_image: Option<&[u8]>,
-    ) -> () {
-        self.code_memory
-            .profiler_module_load(profiler, module_name, dbg_image);
-    }
-
     /// Shared signature registry.
     pub fn signatures(&self) -> &SignatureRegistry {
         &self.signatures