[PWA] Create getAppOsState api for pwa

This is the first API implemented to manage pwa via devtools.

Bug: b/331214986
Change-Id: I5bbc29bdaec6413fc6e96f8ff44b12431b99ccc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5393285


Reviewed-by: Dibyajyoti Pal <dibyapal@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>
Commit-Queue: Zijie He <zijiehe@google.com>
Cr-Commit-Position: refs/heads/main@{#1282042}