Bug 1779421 - Part 3: Add tests for expected module status and async evaluating state r=yulia

This adds a shell function 'clearModules' to clear all loaded modules, so that
tests can be insulated from one another.

Depends on D151834

Differential Revision: https://phabricator.services.mozilla.com/D151835

js/src/shell/js.cpp

@@ -5585,6 +5585,14 @@ static bool RegisterModule(JSContext* cx, unsigned argc, Value* vp) {
   return true;
 }
 
+static bool ClearModules(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  ShellContext* sc = GetShellContext(cx);
+  sc->moduleLoader->clearModules(cx);
+  args.rval().setUndefined();
+  return true;
+}
+
 static bool ModuleLink(JSContext* cx, unsigned argc, Value* vp) {
   CallArgs args = CallArgsFromVp(argc, vp);
 
@@ -9396,6 +9404,10 @@ static const JSFunctionSpecWithHelp shell_functions[] = {
 "  Register a module with the module loader, so that subsequent import from\n"
 "  |specifier| will resolve to |module|.  Returns |module|."),
 
+    JS_FN_HELP("clearModules", ClearModules, 0, 0,
+"clearModules()",
+"  Clear knowledge of all loaded modules."),
+
     JS_FN_HELP("moduleLink", ModuleLink, 1, 0,
 "moduleLink(moduleOjbect)",
 "  Link a module graph, performing the spec's Link method."),