[#6923] Add system-specific adventure importer dialog with actions

[arbron]

Adds a new Adventure Importer sheet that follows the dnd5e design style. Following the example of core with its V2 importer, this sheet is not made default and instead must be opted into on a per-adventure basis.

The new sheet includes support for pre- and post-import actions which are presented as checkboxes on the importer sheet to give control to users. There are three actions initially provided by the system: "Activate Scene", "Display Journal", and "Customize World", but modules can add their own actions.

Each adventure can use flags to define which of the actions is run when that adventure is imported and customize their behavior. There is also a new AdventureRegistry that allows defining actions for a single adventure or for all adventures in a module. Actions added through the registry can support custom handlers without having to add to the global configuraiton.

// These actions will be run across all adventures in the module
dnd5e.registry.adventures.setModule("dnd-adventures-faerun", {
  importActions: ["activateScene", "displayJournal"]
});

// This specific adventure has a different set of actions
dnd5e.registry.adventures.setAdventure("Compendium.dnd-adventures-faerun.adventures.Adventure.OJuc9WnDJDAETIFr", {
  importActions: [{ id: "displayJournal", journalId: "x0TaNijLJkanmufc" }]
});

The system also contains a dialog that presents actions available after using quickstart to load the adventure. By adding a separate quickstart handler actions can opt in to support on quickstarted adventures. These actions are passed all of the adventures that have that action and their configs so they can optimize if more than one adventure is quickstarted.