usingInertiaJS flag on Application

[ThisIsMissEm]

As a package developer, it's helpful to be able to detect your package is being used with Inertia vs Edge.js, right now, there's flags for usingEdgeJS and usingVineJS, but nothing for indicating if Inertia.js is in use.

The reason you might want to know this is to generate correct stubs, for instance, if you do a redirect, you likely want inertia.location(url) instead of response.redirect().toPath(url), or you might want to generate views for the correct engine.

It may also need to be an object, indicating if react or vue is being used, not just if inertia in general is being used or not.

Right now I detect this by checking if config/inertia.ts exists, which isn't fantastic but does work.