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/code_memory.rs

@@ -5,7 +5,6 @@ use region;
 use std::mem::ManuallyDrop;
 use std::{cmp, mem};
 use wasmtime_environ::{Compilation, CompiledFunction};
-use wasmtime_profiling::ProfilingAgent;
 use wasmtime_runtime::{Mmap, VMFunctionBody};
 
 struct CodeMemoryEntry {
@@ -237,22 +236,4 @@ impl CodeMemory {
 
         Ok(())
     }
-
-    /// Calls the module_load for a given ProfilerAgent. Includes
-    /// all memory address and length for the given module.
-    /// TODO: Properly handle the possibilities of multiple mmapped regions
-    /// which may, amongst other things, influence being more specific about
-    /// the module name.
-    pub fn profiler_module_load(
-        &mut self,
-        profiler: &mut Box<dyn ProfilingAgent + Send>,
-        module_name: &str,
-        dbg_image: Option<&[u8]>,
-    ) -> () {
-        for CodeMemoryEntry { mmap: m, table: _t } in &mut self.entries {
-            if m.len() > 0 {
-                profiler.module_load(module_name, m.as_ptr(), m.len(), dbg_image);
-            }
-        }
-    }
 }