Implement basic hot reload (#1741)

Reload any changed modules without any specific order, then reload main
module and call main func to hopefully apply changes.

Still need to get module dependency graph to reload in topological order
and find correct ancessor chain where reloaded modules can be saved in
closures.

Author: samogot

.gitignore

@@ -18,8 +18,8 @@ tool/test_all.dart
 # Ignore extra files from dart2js that we don't want
 build_runner/lib/src/server/graph_viz_main.dart.js.deps
 build_runner/lib/src/server/graph_viz_main.dart.js.tar.gz
-build_runner/lib/src/server/hot_reload_client.dart.js.deps
-build_runner/lib/src/server/hot_reload_client.dart.js.tar.gz
+build_runner/lib/src/server/hot_reload_client/client.dart.js.deps
+build_runner/lib/src/server/hot_reload_client/client.dart.js.tar.gz
 
 # Ignore dazel generated
 .dazel