[dart2wasm] Dynamic modules

Missing from this implementation:
- Closure/dynamic calls with differing signatures
- Overrides with extra optional parameters
- Records with same shape defined in different dynamic modules
- Avoiding running TFA on dynamic module.
- Recompilation of only updateable functions from main module.
- Persist wasm def types from main module.

Testing is currently done locally via the dynamic_modules package test suite:
dart pkg/dynamic_modules/test/runner/main.dart --runtime=dart2wasm

Immediately after this lands we can introduce a new step to one of the wasm test matrix configurations that runs the above test suite (the VM has a similar configuration).

Change-Id: I3386d84be11b773842d45f4268a62a54c47e352b
Tested: Tested via new tests in dynamic_modules package. Tests run locally but will add to existing config.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/397721
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>

pkg/kernel/lib/kernel.dart

@@ -41,7 +41,8 @@ Component loadComponentSourceFromBytes(Uint8List bytes,
   return component;
 }
 
-Future writeComponentToBinary(Component component, String path) {
+Future writeComponentToBinary(Component component, String path,
+    {bool includeSource = true}) {
   IOSink sink;
   if (path == 'null' || path == 'stdout') {
     sink = stdout.nonBlocking;
@@ -51,7 +52,8 @@ Future writeComponentToBinary(Component component, String path) {
 
   Future future;
   try {
-    new BinaryPrinter(sink).writeComponentFile(component);
+    new BinaryPrinter(sink, includeSources: includeSource)
+        .writeComponentFile(component);
   } finally {
     if (sink == stdout.nonBlocking) {
       future = sink.flush();