Implement isDemoSession and isPublicSession flags in app.runtime in lacros.

This CL implements two flags in Lacros in chrome.app.runtime onLaunched event.
Those were previously not implemented.

R=erikchen, jennyz

Bug: 1338773
Change-Id: I3c62c46b9a29c507f0b1db6bc158749641f6542d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3836533
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: David Bertoni <dbertoni@chromium.org>
Commit-Queue: Sergii Bykov <sbykov@google.com>
Cr-Commit-Position: refs/heads/main@{#1038688}