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/c-api/src/ext.rs

@@ -3,7 +3,7 @@
 
 use crate::{wasm_byte_vec_t, wasm_config_t, wasm_engine_t};
 use std::str;
-use wasmtime::{OptLevel, Strategy};
+use wasmtime::{OptLevel, ProfilingStrategy, Strategy};
 
 #[repr(u8)]
 #[derive(Clone)]
@@ -21,6 +21,13 @@ pub enum wasmtime_opt_level_t {
     WASMTIME_OPT_LEVEL_SPEED_AND_SIZE,
 }
 
+#[repr(u8)]
+#[derive(Clone)]
+pub enum wasmtime_profiling_strategy_t {
+    WASMTIME_PROFILING_STRATEGY_NONE,
+    WASMTIME_PROFILING_STRATEGY_JITDUMP,
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn wasmtime_config_debug_info_set(c: *mut wasm_config_t, enable: bool) {
     (*c).config.debug_info(enable);
@@ -88,6 +95,18 @@ pub unsafe extern "C" fn wasmtime_config_cranelift_opt_level_set(
     });
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn wasmtime_config_profiler_set(
+    c: *mut wasm_config_t,
+    strategy: wasmtime_profiling_strategy_t,
+) {
+    use wasmtime_profiling_strategy_t::*;
+    drop((*c).config.profiler(match strategy {
+        WASMTIME_PROFILING_STRATEGY_NONE => ProfilingStrategy::None,
+        WASMTIME_PROFILING_STRATEGY_JITDUMP => ProfilingStrategy::JitDump,
+    }));
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn wasmtime_wat2wasm(
     _engine: *mut wasm_engine_t,