Follow-up to a5497b74be
In the linked commit, as part of simplifying the invite modal, we removed the option to skip sending an email when creating an invite restricted to a specific address. This has caused confusion about whether an email will be sent by Discourse or not, so we're adding back the option to create a restricted invite without emailing.
Internal topic: t/134023/48.
This commit simplifies the initial state of the invite modal when it's opened to make it one click away from creating an invite link. The existing options/fields within the invite modal are still available, but are now hidden behind an advanced mode which can be enabled.
On the technical front, this PR also switches the invite modal to use our FormKit library.
Internal topic: t/134023.
