UX: Simplify invite modal (#28974)

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.

config/locales/client.en.yml

@@ -1964,14 +1964,26 @@ en:
           error: "There was an error generating Invite link"
 
         invite:
-          new_title: "Create Invite"
-          edit_title: "Edit Invite"
+          new_title: "Invite members"
+          edit_title: "Edit invite"
 
           instructions: "Share this link to instantly grant access to this site:"
-          copy_link: "copy link"
           expires_in_time: "Expires in %{time}"
           expired_at_time: "Expired at %{time}"
-
+          create_link_to_invite: "Create a link that can be shared to instantly grant access to this site."
+          copy_link_and_share_it: "Copy the link below and share it to instantly grant access to this site."
+          copy_link: "Copy link"
+          link_copied: "Link copied!"
+          share_link: "Share link"
+          link_validity_MF: |
+            Link is valid for up to { user_count, plural,
+                one {# user}
+              other {# users}
+            } and expires in { duration_days, plural,
+                one {# day}
+              other {# days}
+            }.
+          edit_link_options: "Edit link options."
           show_advanced: "Show Advanced Options"
           hide_advanced: "Hide Advanced Options"
 
@@ -1984,12 +1996,16 @@ en:
 
           add_to_groups: "Add to groups"
           invite_to_topic: "Arrive at topic"
-          expires_at: "Expire after"
-          custom_message: "Optional personal message"
+          expires_at: "Expire at"
+          expires_after: "Expire after"
+          custom_message: "Custom message"
+          custom_message_placeholder: "Add a personal note to your invitation"
 
           send_invite_email: "Save and Send Email"
           send_invite_email_instructions: "Restrict invite to email to send an invite email"
-          save_invite: "Save Invite"
+          save_invite: "Save"
+          cancel: "Cancel"
+          create_link: "Create link"
 
           invite_saved: "Invite saved."