Support breakpoints for hot reload

Adds support for properly reregistering breakpoints across
a hot reload. Like with hot restart, leverages the kPausePostRequest
event in order to reregister breakpoints. DWDS does the initial
work to load the new sources in ("hotReloadStart"), and pauses and
sends the request. Upon disabling existing breakpoint, reregistering
and registering new breakpoints and resuming, DWDS will resume the
app and push the new sources into the runtime ("hotReloadEnd").

Also reinitializes some cached information in order to compute new
sources. Note that it's very conservative for now. A future change
should optimize the invalidation.

Adds tests for the following cases:
- Editing a line with a breakpoint.
- Adding a line before a breakpoint.
- Removing a line before a breakpoint.
- Adding a new file with a breakpoint in it.
- Breakpoint in previously captured code is removed.
- There's no pause when pause_isolates_on_start is false.

Author: srujzs

dwds/lib/src/debugging/inspector.dart

@@ -32,7 +32,7 @@ import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 /// Provides information about currently loaded scripts and objects and support
 /// for eval.
 class AppInspector implements AppInspectorInterface {
-  final _scriptCacheMemoizer = AsyncMemoizer<List<ScriptRef>>();
+  var _scriptCacheMemoizer = AsyncMemoizer<List<ScriptRef>>();
 
   Future<List<ScriptRef>> get scriptRefs => _populateScriptCaches();
 
@@ -68,9 +68,9 @@ class AppInspector implements AppInspectorInterface {
 
   final ExecutionContext _executionContext;
 
-  late final LibraryHelper _libraryHelper;
-  late final ClassHelper _classHelper;
-  late final InstanceHelper _instanceHelper;
+  late LibraryHelper _libraryHelper;
+  late ClassHelper _classHelper;
+  late InstanceHelper _instanceHelper;
 
   final AssetReader _assetReader;
   final Locations _locations;
@@ -99,15 +99,25 @@ class AppInspector implements AppInspectorInterface {
     this._locations,
     this._root,
     this._executionContext,
-  ) : _isolateRef = _toIsolateRef(_isolate) {
+  ) : _isolateRef = _toIsolateRef(_isolate);
+
+  /// Reset all caches and recompute any mappings.
+  ///
+  /// Should be called across hot reloads.
+  Future<void> initialize() async {
+    _scriptCacheMemoizer = AsyncMemoizer<List<ScriptRef>>();
+    _scriptRefsById.clear();
+    _serverPathToScriptRef.clear();
+    _scriptIdToLibraryId.clear();
+    _libraryIdToScriptRefs.clear();
+
     _libraryHelper = LibraryHelper(this);
     _classHelper = ClassHelper(this);
     _instanceHelper = InstanceHelper(this);
-  }
 
-  Future<void> initialize() async {
     final libraries = await _libraryHelper.libraryRefs;
     isolate.rootLib = await _libraryHelper.rootLib;
+    isolate.libraries?.clear();
     isolate.libraries?.addAll(libraries);
 
     final scripts = await scriptRefs;
@@ -702,8 +712,7 @@ class AppInspector implements AppInspectorInterface {
   /// This populates [_scriptRefsById], [_scriptIdToLibraryId],
   /// [_libraryIdToScriptRefs] and [_serverPathToScriptRef].
   ///
-  /// It is a one-time operation, because if we do a
-  /// reload the inspector will get re-created.
+  /// This will get repopulated on restarts and reloads.
   ///
   /// Returns the list of scripts refs cached.
   Future<List<ScriptRef>> _populateScriptCaches() {