Disable Crosh link depending on the policy value

If SystemFeaturesDisableList policy is set to disable Crosh then the Crosh browser link should be disabled (redirected to app disabled page). Crosh is a special case within the other system features, because the Crosh link is accessible through the chrome-untrusted schema, that is why this CL also adds web ui handling for untrusted web ui.

Bug: b:210659944
Test: browser_test --gtest_filter="SystemFeaturesPolicyTest.RedirectCroshURL"
Change-Id: I622e823ece8dd8a8d280df1ab0a17cf95c6bd733
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3427756


Reviewed-by: Christopher Lam <calamity@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Olya Kalitova <okalitova@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968359}