[PWA] Implement PWA.changeAppUserSettings

Now only user display mode and user link capturing are supported.

The noticeable difference comparing to the design doc is the rename of
the API. Now it's called changeApp"User"Settings, as it should change
only user settings; meanwhile the "user" prefix has been removed from
all the parameter names.

Include-Ci-Only-Tests: true
Bug: 331214986
Fixed: 339453269
Change-Id: I0f69ad5e4b8e63d22180a3a667e6f02aa8306751
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5606216
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Zijie He <zijiehe@google.com>
Reviewed-by: Dibyajyoti Pal <dibyapal@chromium.org>
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1319230}