LibWeb: Push the realm execution context before linking modules

This patch adds a non standard step pushing the realm execution context
of fetching client's settings object onto the execution context stack
before linking a module script. Without the realm execution context
there is no current settings object, leading to a crash in
HostResolveImportedModule.

Userland/Libraries/LibWeb/HTML/Scripting/Fetching.cpp

@@ -305,6 +305,8 @@ void fetch_inline_module_script_graph(String const& filename, String const& sour
 // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-the-descendants-of-and-link-a-module-script
 void fetch_descendants_of_and_link_a_module_script(JavaScriptModuleScript const& module_script, EnvironmentSettingsObject& fetch_client_settings_object, StringView destination, HashTable<ModuleLocationTuple> const& visited_set, ModuleCallback on_complete)
 {
+    fetch_client_settings_object.realm().vm().push_execution_context(fetch_client_settings_object.realm_execution_context());
+
     // 1. Fetch the descendants of module script, given fetch client settings object, destination, visited set, and with the following steps given result:
     fetch_descendants_of_a_module_script(module_script, fetch_client_settings_object, destination, visited_set, [on_complete = move(on_complete)](JavaScriptModuleScript const* result) {
         // 1. If result is null, then run onComplete given result, and return.