Bug 1743465: send additional information about existing installations in...

Bug 1743465: send additional information about existing installations in installation.first_seen Telemetry event. r=nalexander, a=RyanVM

This patch does two things:
1) Adds a few new pieces of information to the installation "first_seen" event. Specifically:
    * other_inst - true when any non-MSIX installation other than the running one was present when this event was prepared
    * other_msix_inst - true when any MSIX installation other that the running one was present when this event was prepared
2) Begins sending this event for MSIX installations

Differential Revision: https://phabricator.services.mozilla.com/D134326

Depends on D135246